Hi there, Susan!
You have picked a gorgeous time to come to Walt Disney World, The weather is starting to warm up, so you'll definitely be able to take advantage of your heated Resort pool during the day, while the nights are still cool enough that you might want to bring a light sweatshirt or jacket along for your activities.
After Presidents' Day weekend in February, Disney attendance does see an uptick. School calendars often start spring breaks in early March and roll through April. In my experience, Presidents' Day weekend is the start of the spring busy season.
Do be aware that the
Disney Princess Half Marathon Weekend is scheduled for February 24-26, 2012. Last year, the Princess saw approximately 22,000 runners signed up for the race. While this is a significant number, it is by no means unmanageable, particularly when you consider that these runners and traveling groups are spread out over four Parks, any number of Resorts and their amenities, Downtown Disney, etc. Also, not all of the runners and their groups stayed on after the race; many parties used race day as the final day of the trip.
Have a wonderful time on your upcoming trip!
See you later, celebrator!
-Deborah B.