So things will likely look very different in terms of specs on Wednesday (my guild has an MC run planned, and I can't wait to see what happens). Personally, I like my rogue's combat daggers spec, so I'll probably keep it (he's only 50 now, so I'm not real worried about it). My warrior is currently specced protection, but hasn't been getting much play (or DPS) as a tank, so I may flip him fury or half prot-half fury. My priest is staying shadow, but my shaman -- for the expansion, I'm planning to switch him to elemental instead of restoration, so by Wednesday he may be much more deadly with lightning bolts than healing waves (not sure how that will go over in my guild raids, however).
If you're thinking about respeccing, Mystic Worlds has posted a nice little commentary on how specs work -- while you should really spec for the talents and abilities you play with, for each class there's usually three or four different ways to set things up, either for soloing (or leveling), PVP, or PVE play. Of course, you don't have to respec on Wednesday -- you could just choose the same talents you have in place now. But since everything is changing so much (even your regular spec will have a few new shines to it), this might be your chance to be something a little bit different than you're used to.