Yeah you're right, dispersion is not completly useless, but I just feel like ... having half a talent, let me explain.

I cannot see how this talent will be used for both it's side at the same time. This talent has 2 aspects, and the 2 combined together probably makes it "worth" more, but imo the situations where you will want both 90% reduction AND mana regen will be quite rare; they will happen, but most of the time I feel I will use it either for the reduction, or the mana, not both.

That being said I quite appreciated it a couple of times, it saved my life a few times and it made me able to continue some boss fights without running oom.

For the crit, I would really like to try it out, I'm just not sure how to proceed on this testing. I would probably need to try it out with no gear, with only crit, with only SP, and with SP and crit? I don't mind doing it I'm just not so sure of how to do it

It might be worth re-evaluating dispersion.

Unless you're blowing it at the very start of a fight, you should be able to benefit from 100% of the mana regen when you use dispersion as a defensive measure. If you end up using it solely for mana purposes (I'd avoid this for the same reason mages avoid evocate; loss of dps time) then you're not quite as fortunate, although timing it right before you expect to take standard raid damage can be viable too.

If you compare dispersion to other classes 51 point talents, you'll find that it's not inferior overall. Frost Mages, for example, get a new ability which is not raid-viable (stun a frozen target).

People claiming Dispersion isn't a good talent tend to forget that it can be used easily on any encounter with movement* or phases**. That isn't even taking into account how useful the damage reduction can be. If you assume you will always have enough mana and that you will never make a mistake resulting in taking life threatening damage then it is a bad talent. But that's a pretty terrible assumption to be making.

Besides, where else are you going to put that point?

* Felmyst, Illidari Council, Mother Shahraz, Kil'Jaeden, Supremus, etc
** M'uru, Shade of Akama, Felmyst, Kil'Jaeden, Illidan, etc

It's nice for the fact that we now have three personal source of mana return, Mana Potions, Shadowfiends, and Dispersion.

We lose the ability to cast spells, but our current dots keep ticking, we regen 36% of our mana, and all incoming damage is reduced by 90%. This all occurs in a 6 second period, two dot ticks, 3/4 a MB cooldown, 1/4 a DP cooldown, 1/3 a SW:P duration, etc. If you keep track of anything you should only really lose roughly 2 MF's every 5 minutes.

Presumably Dispersion locks you out of about 50% of your DPS if you look at the *very* general breakdown of Shadow Priest DPS. It's roughly 30% MF and 20% MB, with the rest being DoTs. While dispersed you'll have about 40-50% of your DPS still ticking, and only for 6 seconds. While being able to move. While Mages are Evocating they pretty much stop *all* DPS, and even then an errant bit of damage can ruin the whole thing. With Dispersion, you don't have to worry about that at all.

In reality, Dispersion is a much better mana return ability than Evocation ever was.

It's a situational ability, but those situations are pretty common in raids.

ShadowGreenLight is available from WoWInterface / Wowace / Curse :
- Scan raid for talent information
- At beginning of fight, compute maximum theoretical upgrade available in raid according to talents
- During fight scan target debuffs and player buffs to update a small display from red (do not cast SW:P) to green (all upgrade buffs / debuffs are on)
- Move the display with right button (yes I know it's ugly, my lua-fu is not where it should be)

Suggestions welcome (other than : it's ugly :p)

I disagree - you aren't actually locked out of mind blast if you use dispersion while mind blast is on cooldown.

If you're using dispersion for the mana, the ideal time to use it on a fight like brutallus with generally no movement is directly after a mind blast and while your dots have at least ~7.5 seconds on their timers, ~9 for VT. Since the talent becomes available for maximum mana return at below 64% mana, there will be plenty of good opportunities to use it and only delay a mind blast 0.5s and lose 5 ticks of mind flay, not accounting for haste.

Using this WWS parse of Rage, mind flay was 1,090 out of 3206 total dps over the duration of the fight, so if I had the perfect dispersion (using it directly after a mind blast below 60% mana at the same time you have to move out of a death and decay and all dots have plenty of time left), I'm still doing 2116 dps (~66%, not accounting for the 0.5 delay on blast) while gaining 4300 mana.

So, as far as continuing damage is concerned- dispersion is far superior to evocation, although, on a 12k mana pool evocation will return 7200 mana (900 per second) in 8 seconds whereas dispersion returns only 4300 on the same pool (716 per second) in 6.

However, we can't choose between dispersion and evocation, and I really like the damage reduction with the ability to move / use trinkets & items, so I personally hope we keep dispersion

In all the comparisons between Boomkins and Spriests, keep in mind that Balance got a bit of a nerf in 3.0.3 and we got buffed. It's not been my experience since that patch that Boomkins do "far higher" DPS at 70. We're around the 3k range now in Sunwell gear on a friendly fight, give or take a few hundred either way, and that's about where Balance is too. They do have a little more utility IMO, given that E&M is almost a requirement now since warlocks need their curse for DPS, but I don't think it's a major problem.