Last week Blizzard released a bunch of information about WotLK. Lots of people have commented on that, so I will pass.
However, this does make me think of late 2006 when Burning Crusade information was coming out.
At that time I was in the same casual guild that I am in now. We were late getting to the raiding party then, as we are again now. The decision was made that we should try a 40-man raid. We all went and got attuned for Molten Core, set a raid date and… never went in. Blizzard released info about Burning Crusade just as we were ready to pursue raiding. Once it was obvious that expansion was going to be a gear reset, a lot of folks lost interest in raiding. There were some that still wanted to play for the experience rather than the gear, but not enough to make a raid.
Will that happen now? I have been in exactly two 25-man raids, and suddenly WotLK info hits the internet. Will raiders stop raiding? Once a release date is announced, will everyone just farm gold and level tradeskills in anticipation of the expansion? I hope not.