According to several sources including the Washington Post tourists to Florida are being warned not to offend Florida residents because a new law on the books, as of October, makes it easier to claim self-defense in a shooting. Residents can even apply the same criteria to shooting someone in their car as they would to someone invading their home - a change intended to thwart car jackers.
But protection from car jackers or tourists is not what this is really all about. My guess is that this law is really intended to allow wealthy republicans to protect themselves from angry disenfranchised Florida voters.
UPDATE May 2012 seven years later: Google Travon Martin and see what a circus this law has caused.