Hi guys,
We have been in Orlando every Feb for the last 7 years, most of them over Presidents Day weekend. The americans tend to take this as a long weekend so this means the crowds are heavier from the Friday through to the Tuesday. Mostly this has an effect on the main Disney parks as this is where the Americans tend to head (they tend to stay onsite and stay in the Disney parks) By Thursday they have gone home and the parks are much less crowded. We made the mistake a couple of years ago of going to MK on the Wednesday and it was a nightmare compared to our second visit a couple of days later....a lesson learned!
With this in mind we usually stay away from Disney for those few days and do Seaworld, Kennedy Space Center or Universal - as Wendy mentioned, the water parks tend to be a good choice too although Blizzard Beach is normally closed, TL will be open.
With regard to weather - it's usually like a British Summer which means temperatures can go up to 80 but can be as low as 65. Thunderstorms aren't as common as in the summer but the rain can be heavy and it can be chilly in the evenings. We usually pack shorts, t shirts, light trousers and a fleece for throwing on in the evenings.
A good tip is to watch the Weather Channel in your hotel room/villa - these guys are very accurate and you can then change your plans to suit the weather. (i.e. if they say it's going to rain then don't plan a water park)
Don't forget the Mardi Gras parade at Universal which is great fun with live concerts on on Saturday nights.