Since I've subscribe to TourGuide Mike, I no longer worry about crowds. I'll be there this coming President's Day weekend (I just booked my flights a few days ago). I was there Christmas 2009 and had a great experience. If you're interested in TGM then subscribe by clicking through the ad on the Theme Parks board (TGM is the board's sponsor) and you'll save $3. I'll never take another WDW trip again without TGM.
Crowd-wise, the way I understand it is that it should be a bit less than Christmas, Thanksgiving and Easter but pretty close to the rest of the holidays you mentioned.