I tried to quest a bit on beta with a shadow priest, it's so unsatisfying. Losing DP and having to shadowmend after each pull is boring, it's made of paper and shield helps little to nothing, also void form when questing is pretty much wasted for most of its duration. There is also the fact that when I use Eruption to enter void form, I find Void Bolt on the Global Cooldown and I don't understand why, it's should be immediately available since Eruption has a casting time. Anyway it's not really a smooth experience, even though my shadow priest is item level 720. I know they perform well in raids, but for questing it was quite bad and not really fun.