Out of curiosity, I occasionally check the search engine queries that bring people to my weblog. For example, I've discovered that some traffic, consisting of people with peculiar interests, has been directed therein by a post I wrote defending incest and bestiality prohibitions.
I ran across an two month old ABCNews article, pointing out that if the Supreme Court judges rightly in Lawrence v. Texas and deems laws against sodomy to be unconstitutional (discriminating against men either facially or practically), the designation of "gay" may cease to be considered defamatory per se, and people suing for slander or libel because they have been called gay will have to prove actual damage.
As long as sodomy is illegal, a sexually active homosexual is a criminal. The continuing public condemnation of homosexuality, however, may mean that "gay" will remain defamation even if sodomy becomes constitutionally protected.
I didn't know that you could sue someone just for his saying you were gay, unless you could show at least some possibility of damages. I've had people -- gay people, actually -- call me gay, and I never thought that I was being defamed. Of course, this happened at a large public university with moderate attitudes about homosexuality and a healthy Queer Student Union; I might have been more disturbed by it had it occurred when I was living in a small, conservative town.
The geographic differences that make calling someone gay in D.C.'s Dupont Circle an honest error, and calling him gay in rural Virginia per se defamation, imply that libel and slander suits will have to rely on community standards to determine whether they are viable.
One could look at whether a community has businesses specifically oriented toward gay people that operate without being molested by the authorities or community members. In Charlottesville, for example, the only dance club in town, Club 216, is a gay club. I've never heard of its having problems except when too many straight girls show up on College Night. Thus being called gay in Charlottesville would be defamatory only if one could prove that it had had a negative economic impact.