Wind currents in the northern Gulf of Mexico where the well is flowing tend to drive north and northeast, hence onshore, before any of the Loop Current waters flow out between Cuba and Florida into the Atlantic portion of the Stream.
Coastal areas of the northern and eastern Gulf would be devastated before then. If the spill fluids do enter the Loop and on into the main Gulf Stream, eastern Florida beaches and shore biota would be devasted.

http://www.oceanweather.com/data

National Geographic News, May 4, 2010
http://news.nationalgeographic.com

From National Geographic News:
"There's no predicting the exact movements of the oil spill- which is growing ay at least 5,000 bbls./day. But winds could push the slick south, where oil might get swept into the current."
........"If oil is swept up in the Loop Current (1-2 meters/sec.) "there's essentially no way to stop it" (T. Sturges, Prof. Em. oceanography, Florida State Univ.).

The coast could be affected as far north as Cape Hatteras.