For me, the reaction has been almost the opposite-- my guild is pretty energized lately, and partly because of the expansion. We're hurrying to get into the endgame dungeons, and personally I'm putting in a lot of time trying to get my alt up before the December patch hits. But this problem is more widespread than even Blizzard might admit-- also on Livejournal, Thena B says she just can't find the urge to play WoW when everything is changing in just a month or two. Why play characters now when everyone's going to be rolling new characters as Draenei and Blood Elves?
I've said before that just because the expansion's coming out doesn't mean the game we have is any less fun-- I'm still enjoying myself. But I can't argue with experience, and lots of players are saying they just plain aren't feeling it lately. Is the game (and participation in general) slowing down because of the imminent expansion release? Are you playing more or less when you realize that almost everything is Azeroth is going to drastically change in the next few months?