A large downwinder was fun such as Neil organized last year from Jupiter to Ft. Lauderdale. Not sure if he is planning another one this year, hope so. More about last years effort at:
http://fksa.org/forumdisplay.php?f=64
It would be fun to try to do a run from Miami to Key West or vis versa. I am not sure how feasible this would be from a wind direction standpoint however. I don't think anyone has done the entire run yet successfully. The curvature of the Keys can be a real bugger in sorting out viable winds for the entire run from a single direction.
This question would be best fielded by an attorney. That said, here goes, if the organizers are offshore, the liability and lesser quantities of it may stay there. On the other hand, if some or all of the organizers, sponsors reside in the USA, it wouldn't be much of an effective means of avoiding liability.
We had a similar problem in finding insurance for the record Key West to Cuba crossing in 2001. They wanted insurance for the effort, but all I could find was coverage within USA territorial waters. Once they kited beyond those waters, the coverage stopped but the liability did not unfortunately. Good news is the crossing came about, with some injuries and damaged gear but fortunately out of control liability issues did not arise.