Well, some initial information has been released on Cataclysm's dispell mechanics, mostly from the perspective on how the changes will affect Healers. Basically, there are going to be 5 types of "dispellables". Diseases, Poisons, Curses, Defensive Magic and Offensive Magic. Each healer will be able to remove three types of the bonuses. The mana cost of dispell abilities will rise significantly, and all "no thought" mechanics are being removed.
What this means for priests is that 1) we don't get any new types of dispell ability, 2) Abolish Disease is going to be removed from the game and 3) Shadow Priests will be dropped out of Shadow Form when we cast Cure Disease.