You need to think about Presidents day (Washingtons birthday) as well.
Presidents day falls on the third Monday in February and a lot of people go to Orlando for the weekend.
I went to Orlando in February about 5 years ago and generally it was quiet except for Presidents weekend.
For the Presidents weekend we found the parks very crowded, but as we were there for two weeks it was not a big problem.
I have to say February is a great time to go as the parks are quiet and the weather is generally very good (you do not face the heat and humid weather in like in July & August)
More on presidents day here:
http://familyinternet.about.com/od/holidayfun/ a/presidentsday.htm