Ditto to what everyone else said.
Weather is most definitely luck of the draw. We flew last January 26, and although it was c-c-c-cold, there were no problems. I flew solo in April and had to wait for the plane to be de-iced, so you just never know.
One more note on connecting flights versus non-connecting flights. If you are taking a flight with a connection, try and make your connection through that airlines southernmost hub. That way if there are weather delays, and planes are having a hard time getting around, you stand a better chance of getting where you are going with a 'hub' connection, since they may be more likely to have planes there. Just a thought. (i.e. Delta or AirTran through Atlanta, USAirways through Charlotte, etc).