Dispersion is a talent that Shadow Priests talk about a lot. The vocal majority hates it. The vocal minority loves it. The general populace... uh. Who knows. They don't talk. Me? I'm not awed by it. I also don't hate it. In fact, I've spent talent points in it and will continue to do so, and I find it fairly useful. It just doesn't amaze me.
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.