I just came back from a trip to St. Pete, and here's what we came across (I flew down and drove home w/my parents who had been there since January). There was a LOT of construction on I75, especially between Macon and Atlanta. At one point, the southbound lanes were backed up for miles to to a lane closure - this was right around Atlanta, but I don't remember if it was north or south of there. Gas prices weren't too bad. A couple of places were $0.99 for regular, but I think we averaged $1.09-$1.12. This was on March 6-8.
We are going to WDW later this year, and were planning on driving (I actually do most of it, and really don't mind it - I think it's a control thing!), but after seeing all of the delays heading south, now I'm thinking that if I can find a good airfare, we may just fly.