As you all know by now, patch 3.1 will be a big one. Bringing a new Raid Instance, class changes and dual speccing !
Patch 3.1 will represent one of the most significant content patches to World of Warcraft to date. Major modifications to class specializations via the new dual spec feature will bring about significant game play changes for many classes, while the introduction of the Ulduar raid will open up a new and more difficult tier of raiding.
Wowinsider has a guide to documented and undocumented changes. Ofcourse it’s still early and a lot of things can still change: