Last year, I recall people were shocked by the horrible crowds prior to Thanksgiving, and then pleasantly surprised by smaller crowds AFTER Thanksgiving, due to AP blockouts. Even Deluxe APs are blocked out Thanksgiving and the two days after.
With the economy doing (marginally) better and perhaps fewer people renewing their APs, blockout dates may not be the massive deciding factor they were in 2009. But I thought I'd throw that out there, as they still have an effect. The idea is that many tourists will be with family for Thanksgiving, and many locals may be blocked out (or just plain spending time with family away from Disneyland). I'm not sure if this applies in 2010 like it did in 2009, but that's what I'd be betting on if it were my trip.
I DO know that in most cases, non-blocked days + kids out of school = massive crowds. So, I would personally avoid the days before Thanksgiving like the plague.