Dispersion definitely has a PvP slant to it. If you arena or BG, you're going to see it as much, much more awesome than people who PvE almost exclusively. In the arena, it's just a good talent, especially once they changed the talent to be able to be used while stunned, feared and silenced. Foiling a stunlock or an assist train can be enough to take the wind out of your opponent's sails. Obviously it requires your partner(s) being able to play off of it as well, but I'm fine with that. PvP should be about the team, even if you're just in a battleground.
PvE is a slightly different case. Its applications are more questionable. And if not questionable, debatable. Mana regen is nice, but do we need it? Damage reduction is helpful, but will it actually come into play? Fair questions! I'm not here to give you absolute answers. I don't think there are absolute answers. Do you like it? Do you not like it? That's what it'll come down to in the end. What I can try to do is give a few examples of what it has done for me, and my opinions on its usefulness.
Primarily, it helps out immensely in those, "oh mother of Uther I am the biggest moron in the world" moments. For example, when your camera is tilted all the way up trying to DoT up Shield Orbs on Kil'jaeden and miss the raid announcement and casting bar for Darkness of a Thousand Souls and don't notice it until it's too late. That AOE that was going to one-shot you? Meh. Who cares? It's gone now.
Are you in a 5-man dungeon with a new tank, and they pulled something wrong? Like... oh, I dunno, an entire room in Shadow Labyrinth? And suddenly you're tanking two mobs, and after many minutes of stressful combat you find you're out of mana? No problem. You now have mana and a little bit of a break from getting pounded on.
Looking at those examples you can say, "Well if you don't play like an idiot you can avoid those things." For the most part, you'd be right! However, mistakes happen. Especially when you're first learning an encounter or a dungeon. When you first do a boss, there are always unexpected elements. If your health is suddenly dropping, hit Dispersion, all better. Even if things are expected, but they're relatively new to you, you might forget or not quite have the strategy down. Dispersion can pull you out of the fire.
Dispersion doesn't change the Shadow Priest class (spec, whatever). Not nearly. However, it does help. It does have an effect. Mana regen aside, raiders will find a use for this, I have no doubt. Buffer against wipes? Uh, yes please. How many raids would have adored that on Archimonde, hm? Archimonde is the Super Bowl of various oopsies wiping the raid.
As a leveling tool, I would personally recommend this talent to everyone. Really. Truly and honestly. It makes grinding fantastic, and I've talked about it in that context before. The mana regen, the damage reduction, the whole shebang. I honestly think you're hurting yourself if you level Shadow and do not pick up Dispersion.
Did I ramble enough? I think I rambled enough. Like I said, my point here was not to convince the world that Dispersion is some amazing, perfect talent. It isn't. There's a tremendous amount of hate for it going around though, and it's really not that bad. 'Oh crap' buttons are always situational, but that doesn't mean they're bad. Aside from Shadow Priest DPS, one of our weak points since The Burning Crusade launched has been our survivability. Well, here's some survivability. In the form we wanted it? Not necessarily, but we got it, so put it to good use eh? Spec it. Try to love it. It loves you!
Oh, and it looks super cool. Seriously. Do you see that screenshot up there? It's awesome. I would spend a talent point in Dispersion just for that if I were you.
Want to find more great tips for carrying out your Priestly duties? Spiritual Guidance has you covered with all there is to know!And don't forget to check the WoW Insider Directory for more priestly info!