No one knows what's going to happen, but it maybe a really good time to go to that area. The hotels in that area are usually at a 86% occupancy rate at this time of year. Right now, they are only at 18% occupancy rate.
It goes without saying that there are some really good deals on vacations in that area. Many of the hotels have slashed their prices by almost half and those are just the ones on St. Pete (Beach).
I've seen a map of where the oil is right now and it's far from the St. Petersburg/ Clearwater Beach area. The spill is up North more.
I would think that you'd be safe going anytime within the next month. Be aware that many airfares require 14 days advanced purchase on the lower fares.