We have gone the last two years during this time. Pres. weekend is very crowded (or so I hear - we have arrived on Mon. or Tues of that week.) The crowds lessen as the week goes on. 2003 wasn't too bad, this past Feb it was much more crowded but where we were was not the wall to wall people Fatcow encountered. There's definitely an ebb and flow and when we'd go somewhere and it was crowded, we'd just go somewhere else. However, this was our 9th trip. If it had been our first, where every PS was scheduled and we wanted to "see it all" I would have been horribly dissapointed. During this week this year almost all the "main attractions" in the parks had 45+ (or+++!) waits and fast passes were gone by mid day. But many of the secondary attractions were not that bad at all. If you're going to consider this, consider the following:
If it's crowded, the MK is always more crowded, so if your kids are ages that Mk's important,this might not be the time to go.
Airfares to fly down and back on the weekends will be expensive. This past year I never saw it for less than about $350RT. That's how we ended up going down 2/16, but not back until 2/25. We paid about $180 RT. If you decided to "extend" the days to get cheaper flights, you'll find the parks much less crowded the week after Pres. Week.
You probably won't get any substantial room discounts PRes. Week.