We've talked before about using Wrath of the Lich King as an opportune time to switch mains. As Daniel mentioned in that post, I'm planning on switching from my human warrior to my draenei warrior once WotLK comes out. Now, one of the things I've noticed from reading forums, talking about it with my guild mates, and of course from you commenters here at WoW Insider is that there seems to be two or three camps of opinion on how to go about switching mains at the expansion.
Camp one we'll call the laissez faire approach. These people, although they intend to switch mains, aren't really doing much about it. They expect that the gear reset from Wrath will take care of any gearing inadequacies and that we're all going to be running around in clown clothes anyway for a while.