No one should be thinking of down ranking, ever. Your argument makes no sense. Yes, you have proven that at a higher mana pool the return from rank 1 is the same as max rank with a lower mana pool. Plug in the rapture return numbers of a max rank at the 24k mana mark, add in the 70 mana saved per cast, then add the optional heal from glyph and let us know what you get. Better yet, don't do that, spend the time contemplating why we are wasting time even commenting about this ludicrous, unplausable mechanic.

Quick question (answer might be buried somewhere in this thread) : is improved PWS talent fixed in 3.1 ? At one point I know the return on investment was really poor...

I did an Undying attempt last night with my guild and while we did very good, it was devastating to fail at Kel'Thuzad after a flawless run...

We were running with a group of 3 healers, me (disc priest), a holy priest and a resto druid and we had a disastrous frost blast spreading to both the other healers just after one of them had moved due to a void zone.

When I realized I was the sole healer responsible for saving them, I sort of panicked and ended up hesitating a bit too much. I did a bit of combat log digging (from this parse: Wow Web Stats )

This is the chain of events :

T = 47.468

T + 0.000: Frost Blast on Riotstar (5489)
T + 0.001: Frost Blast on Goldentung (5087)
T + 0.805: Frost Blast tick on Riotstar (5488)
T + 0.805: Frost Blast tick on Goldentung (5088)
T + 0.808: Fathermerrins Glyph of Power Word: Shield heals riotstar (+1146)
T + 2.012: Frost Blast tick on Riotstar (ABSORB)
T + 2.013: Frost Blast tick on Goldentung (5088) LETHAL
T + 2.823: Frost Blast tick on Riotstar (4765, 724 absorbed)

Riotstar (the holy priest) survived, while Goldentung, the resto druid, died due to my panicking and hesitating too long.

Obviously the most important lesson is to respect the distances and never go too close. But in the event that it DOES happen, is it possible for one healer to save two people, even without circle of healing?

Looking at the chain of events, what really screwed us here is me taking so much time to react initially, that's the sole thing that would've done it. I simply wasn't prepared for the horrendous event of the two other healers getting frost blasted and the panic I felt when I realized that the two people that got hit were BOTH healers and that I was the only remaining one was what caused me to hesitate for a whole 0.808 seconds. That felt like a lot longer last night I can tell you.

The correct response for a disc priest in that situation, I think, (holy would, like I said, save the day using a single CoH) would be PW: S on the first target, followed by a Borrowed Time hasted Penance on target #2.
This does not cover the eventuality that PW: S and/or penance might be on CD and that both targets might have Weakened Soul on them. If that happens, the disc priest is probably screwed. But let's assume that neither of this happens (which is actually the more likely outcome, since with the gear level of our tanks, I don't need to be chaining PW: S and Penance on every cooldown, far from it).

My Penance hits for an average of 3.2k (non crit) per tick and with
Borrowed Time it ticks with a period of roughly 500 ms. Given those numbers, you'd probably need two ticks of Penance to land to be safe, meaning that it must be cast no later than 500 ms before the last Frost Blast tick (and that's cutting it close). Working backwards, this means that the initial PW: S must be cast within:

2.013 (Goldentung death) - 0.5 (penance tick time) - 1.05 (borrowed time hasted gcd) = 0.463 seconds

Which should be quite easily doable, given that you're properly mentally prepared for the eventuality that this could happen, which I'm ashamed to say I obviously wasn't.

Is this the correct response to this situation, or is there a better way to handle it?

As you said the problem was that you were not prepared for this. A Pain Suppression on the druid followed by a PW:Shield on the priest would have saved both of them or if PS was on cooldown just shield one of the PoM and flash heal the other (if penance on cd) the probability that both of them have Weakened Soul is very slim since you already had 2 raid healers to take care of the AoE dmg. Granted I'm holy spec but the first thing I do when a chain ocures is cast PoM since they were chained (they are close to each other) its highly probable that PoM will jump between them and for me it heals enough to save them only from that but of course I wont risk it and I follow up with CoH and flash heals to top them off.

Your druid was not full HP, according to the logs. That is the first reason of your problems.
KT is a boss were you want all your members to be full HP when frost tombs are expected.

Second trouble is, as your said, that you had ranged too close. Range should never be caught in a Ice tombs chain, and especially for healers, that can (should) spread at different raid places (so that to cover the raid, not to be caught at the same time in void zones, and be reactive for healing OT at the beginning of P3).

It is really possible to save two person alone as Disc. healer.
Easiest solution is to PW:S the first, and penance the second.
But you can also POM the first one, and PW:S the second (if penance is on cd, and preferably in this order, as POM heals after damage and PW:S prevents damage).
You can flash heal one, and use any instant heal (penance / PW:S) on the second. Or flash heal both, but that's more challenging.
And you have pain suppression, in case of real emergency, which is off GCD, and is enough to save one target.

Sorry to mess with your priestly ways, but as a paladin flash of light on A > holy shock on B does the trick.

So Flash Heal the first, and PW:S the second, total time taken: 1.5s (reduced by haste).

You could also pre-shield a few of the more closely clumped melee throughout the fight since you know there's a chance this will happen (and since even if they don't get frozen, they'll get frost-blasted anyway).

So , a blue post said rapture from multiple shields is a bug, at least not intended, will we get enough mana in Ulduar without it ?

My usual job is to take care of healing tombs and such whenever we've gotten an undying or immortal run.

I actually open with PoM if it's a chained tomb, because odds are very very high that it is going to bounce to a person adjacent in a tomb, and then to the next person...

Once tombs are potentially coming I keep everything off of CD and heal exclusively with flash and greater. On a single tomb I just shield/penance, and on a chain I usually PoM, shield the (then) lowest one, and then penance the third. If it's real sketchy I use pain suppression in there somewhere as a replacement.

The blues are not talking to eachother on this issue at all. It's getting quite ridiculous. I accept there's a certain amount of communication issues that will arise, but cooldowns do not just go away. Someone has to remove them, and for a specific reason.

Today I was getting enough mana as disc, but I think the bugged rapture is currently live (I didn't check with a stopwatch, but I was shielding a ton on the raid for Razorscale, and my mana bar wasn't moving down that fast). I think disc will definitely have to be a little less spammy in its heals, but overall my take is that there's not really a huge issue.

Disc is viable, but I think disc priests want a holy dual spec at the moment, because disc is a very niche healer. The niche is great if there's RNG damage to single targets (shade of Aran style) or huge tank hits very suddenly, but if the fight is an AOE damage fight, or just a consistently hard-hitting boss, disc is going to decline in usefulness.

P.S. I CANNOT track down a Glyph of Penance at the moment, so take this with a grain of salt, as a Glyph of Penance will make Disc better.

I hope to have a new 3.1 Disc Compendium and a spreadsheet available very shortly.

Generally speaking until I can post full details...

Stat Weights for Output
SP > Haste >= Crit > Int

Haste vs. Crit Rating can be debated... Though my research, testing, and math clearly shows that haste is slightly superior as long as you gain full benefit from the haste. Due to BT it is easy to reach the "soft cap" so less haste is required by Disc overall.... Stacking either haste or crit at the detriment of the other stat is a recipe for lower performance, don't do it. Int is marginally considered as a output stat due to the crit% conversion though it isn't something that you "gear for" because it is on everything you will use. I note Int here because it shouldn't be overlooked that Int does improve your output & regen for thorough discussion.

Stat Weights for Regen
Int > Spi >= Mp5

If you plan to use the same gear as Holy spec on occassion choose Spirit. From the gear currently known there aren't many choices where you can actively choose to not gain Spi in favor of Mp5 so it isn't a huge issue just yet. Though for Disc specifically there isn't a overwhelming reason to take Spi over Mp5.