Ok first off, I'm a bit reluctant about creating a new thread just for a few simple questions, however every paladin I know I asked was either clueless or just not interested in knowing, and the best place to ask stuff seems to be here.
These questions might be a bit technical, and while I'd like to just go and test them myself, Blizzard didn't feel like granting my wish for premades this PTR.

Now, what I understand:
Concentration aura gives you a base 35% chance not to get delayed by damage when you're casting. It's the usual bonus every healing classes(or close to, not sure druids got one) get somewhere in their talents, to prevent getting interrupted on fights like vael or in pvp.
The talent is a 2part talent, the first part simply raises this chance by 15%, making it 45% chance not to get interrupted, stacking with normal bonus.
My questions are about the 2nd part of the talent.
The tooltip says it gives a 5(15 fully talented)% to resist Silence and Interupt effects.

The resisting Silence part I understand quite well, the best example is direct shadow priest silence. However I'm wondering about the interupt part.
When you actually resist an interupt, say a counterspell or a shield bash, do you suffer from the side effect of school locking? Does your spell finish but you can't cast anything as if you didn't resist, or does nothing happen at all?
And when someone uses an improved interupt ability, which usually have a silence ability, say Improved Kick(2s silence) or Improved Counterspell(2? secs silence), are there 2 checks to see if you resist, one for the interupt and one for the silence, or are they rolled into one and you have a 15% flat chance to resist all of it?

I'm trying to figure if there's a point in taking this talent for PvP, considering that if there's 2rolls on improved CS/kick, it might not really be worth it, since a lot of people do have these in PvP builds, and well, getting lucky twice in a row is too much of a gamble imo.

I was specced improved concentration aura for a while and I remember multiple occasions where mid cast I would get earth shocked by a shaman and it would damage me but not interrupt/silence or anything.

As for your second question I'm not really sure, hard to tell without doing any testing.

If you resist the interrupt, it doesn't lock out the school.

I've never gotten silenced if I resist the interrupt for the few months I've had the talent when I was PvP'ing, so I've always assumed there was just one check. I haven't done any type of controlled testing, so I could be wrong though...

That's interesting.

I wasn't aware you could EVER seperate those two effects...does a shaman ES on a priest (with thier -silence talent) ever hit for full damage and not shielded? keep in mind it doesnt' silence if you have a shield up and you don't take any damage.

ES isn't flagged as a silence effect. I'm confused. ><

Anyway, from what I've seen binary spells typically have a primary effect that all other secondary effects are linked to. ES interrupt is linked to damage, so if it's mitigated/resisted nothing happens. Ditto with talented CS. My pally runs with imp. conc aura and I've never been silenced but not spell-locked in many moons of BG grinds.

Raises resist for both interrupt and silencing effects. Things like imp CS and imp shield bash were problematic though at least last time I specced that since you have to resist both parts.

Now not having the talent doesn't mean you can't resist effects, you just don't resist as much.

edit:

I guess they fixed that part.

But it's flagged as interrupt, like pummel.

edit2:

This is how I guess they fixed it - they made it so you binary resist all spells flagged as silence/interrupt. It used to be just the silence/interrupt part hence the imp counterspell thing - you could resist spell lock but the silence would get you or the other way around either way it doesn't work out for you.

It is interesting to hear this from a paladin's perspective. From a Mage's, a 15% chance that I'll waste a GCD and not get a spell-school lock is pretty huge though both in soloesque and group/arena PvP.

I'm not saying that one should run with it as the aura of choice but if you are using it, then the improved talent is not exactly minor. I'm no huge fan of relying on low percentage procs to win but it could certainly turn the tide on occasion.

I guess it's just a matter of playstyle. I try to avoid relying on talents like that or stoicism or any similar talent that gives 5-15% chance to avoid something. Hell, I run with CAura on just because I don't think 70% chance to resist casting time interruption is enough to rely on. Anyway, imp conc isn't bad, per se, it's just not something you can ever rely on. Worth it if you have nowhere else to put points, though, and it might swing the odds in your favor on occassion.

When I was pvping, I ran with conc aura all the time. Never specced imp conc aura, although if I was required to go to BoSanc for raiding I'd probably go through ICA on the way, but it's not a talent I'd go for in it's own right, unless you're trying to build a pure pvp healing build, in which case you'd probably go 33/18/0 or similar.

edit: @Aramul - the 35-50% raise in damage-interruption is useless in most conventional specs as you said, because it's overkill. However, if you only go enough in holy for Spiritual Focus, speccing ICA means you can drop one point in Spir Focus because with Imp. conc and 4/5 Spiritual Focus you're still over 100%, which means you can pull out some oddball specs like 9/31/11, or 9/21/21.

Well the thing is, contrary to the Stun or Fear resist stuff, this one is an aura, so if you get improved conc aura, you share the 15% chance to resist stuff with everyone in the group, mages priests druids whatever. I also found that the fear/stun resist mechanics on my priest was quite useful for PvP, it doesn't proc all the time, but it procs often enough to be annoying for your opponents. Wouldn't be that useful for a paladin with the bubble and plate armor+shield I guess tho, people probably try to kill you last and keep you silenced/counterspelled, thus my questions about this aura.

Seems no one has a definite answer on the double check for improved cs/kick/shield bash stuff, guess I'd have to test it by myself once I level my paladin ^^.

To a frequent PvPer like myself, talented Conc Aura is insanely annoying. Trying to prevent Alliance healing is no walk in the park even without the aura in use. Like the very small chance to miss there always is, % to resist interrupts is one of those things that always seems to happen much more than it should (we just notice the oddities more, I know). Definitely don't disregard it as a talent if you PvP a decent amount, little numbers go a long way.

It's additive.

Take a paladin with Spiritual Focus and Concentration Aura to Deadmines. Gather as many mobs as you can. Cast a heal on yourself. With a gazillion mobs hitting you, if there was any chance of an attack interrupting your heal, you should notice. (Multiplicative percentages would yield a 15% chance to be interrupted) Testing has shown that the mobs will not interrupt you.

The aura is additive. so yes 70+35 = 105%. Paladins with SF and untalented Con Aura cannot be intterupted by damage. IMHO 10 points in holy for SF (or 4 if you getting the talent) are required for any kind of serious pvp.

The problem more than anything is its placement, currently about the strongest pvp talents that we have are very spread out (Guardians favor and Imp Concentration aura in prot, SoComm and Repentence in Ret, SF is holy). Come xpac you could spec 12/18/31 or some varient (which Im storngly considering.) But right now going for Imp con aura is just too many talent points into the currently pretty weak prot tree so you only usually see reckbomb paladins running around with it.

But having it does make Shazz easy mode. =)

IMHO SF should be moved back to teir 1 in holy which would open up more build options for paladins.

But I digress, yes if your going full pvp healer route its a good pick up, and that teir of prot is really strong (imp HoJ and imp Con Aura are just great) but it is pretty deep into prot so at that point you might as well go deeper and get reckoning, etc.

Well I was thinking of doing something like a 40holy/21prot, with imp righteous fury for a passive 6% dmg reduction(until dispelled), imp conc aura, toughness and stuff like that, and use a shield anyway so SoCommand wouldn't be that great. However, I'm debating if imp conc aura is good enough to justify going that far down the tree, or only go for 7-10points in prot and the rest in ret to get 8secs judgements and SoComm for some 2h fun against casters.

No one seems to have done tests with imp CS/kick/bash tho, but iirc, when you base resist a CS or dodge a kick, you don't get hit by the silence part of it, so maybe it means they're linked as one and you have a 15% chance to resist it as a whole, which is worth it, especially as an aura.

imp conc aura is a must for support in group pvp. It was pretty buggy for awhile there but last time I spec'd holy/prot and pvp'd heavily in wsg it was working well. It's additive 105% to avoid casting time interruption meaning you can normally drop a point out of spiritual focus for a bit more flexibility.

Ages back doing shazz when after patch 1.9, I noticed resisting his silence/cs quite alot.

I actually did do some testing with Conc. Aura awhile back, whenever a mage friend and I would wait in the BG we would go out to IF gates and test it out. He had Imp. CS and I had fully talented Conc Aura. I wish I had the scrap of paper I was tracking the results with =(. I was going to see the effect of arcane resist and spell penetration. Anyways, I seem to remember resisting somewhere in the neighborhood of 40% of the silence effects, and around the expected 15% of the interrupt effects of counterspell. What was interesting was, I never resisted just the interrupt. It was always one of three results:

1) Counterspell goes off, spell interrupted/holy school locked, silenced for 4 seconds.
2) Counterspell goes off, spell interrupted/holy school locked, NOT silenced(not that it matters for paladin =/)
3) Counterspell completely resisted.

There are a few builds that make use of ImpConc with only partial SF, but honestly, those are some oddball builds. HS/SoC and BoSanc/Sanctity are pretty out there ;P.

When I had the talent, I just never noticed it to go off. Purely a perception thing; when used against a person procs go off too much, when used by a person procs don't go off enough. It's not a bad talent by any means, but it isn't a cornerstone talent the way the Reckoning, SoC, and SF are.

Example:

Casting holy light
> CS/Silence/Kick/etc here
Still Casting holy light
Holy light landed
Holy School is locked

I don't recall that happening ever. My experience is when you don't get interrupted, you can't get locked.