We're from NH and our school vacation week is the last week of February.
In 2007 we traveled Sat 2/24/07 thru 3/2/07. It was very busy the first day Sat 2/24/07 (then again it's a weekend day too), then got much better with minimal wait times on most of the rides as the week went on.
As the PP mentioned, MG and Presidents week fell the same time in 2007 - so that was a major factor in seeing the increase in crowds.
Some of the family took a side trip to SW on 2/27/07 and felt the crowds were fine there.
In 2009 MG will be 2/24 during our next trip, so we'll need to make sure we have a good plan just in case it's busier than what we experienced last time. Hopefully President's week in 2009 will be manageable for the fellow New Englander's here traveling to the world.
Here is a post I read in the past few weeks that has an interest poll:
http://www.disboards.com/showthread.php?t=1748721.
Just have a good touring plan in place for whatever parks you visit; inside and outside DW. Start early! I know vacations should be a time for catching up on sleep, but it's not easy to do when you're in Orlando!