Improved Initiative has a great post up about how real attempts to roleplay a character that's not like you, the player, can have some amazing effects on you (the player's) ability to empathize with others. What started as a straight white man playing a pretty stereotyped barbarian from an Africanesque background turned into a huge learning experience for the player. Sounds like it didn't start that way, but by the end a fully fledged new personality was created.
As a gay gamer at the RPG table, I relish in being able to take on the role of straight males. But, I must admit that I have a tendency to play up their sexuality as well. This street works multiple ways. My characters' sexuality should be an important part of their background, but it shouldn't be the end all, be all of who that character is.
When I next play my lothario bard Rhyss, I'm going to do some thinking about good ways to bring in other portions of his personality. He's passionately dedicated to his music craft and to freeing his people from oppression. He misses his sister terribly and he's mortified that asking his teacher the wrong question at the wrong time is what sent his teacher off a mental cliff into madness. I think I need to spend some time thinking about how those aspects of Rhyss' life affected his personality. He'll still be after all the ladies, of course, because that's a form of combating discrimination he faces as a midget. But, he'll be doing it in a far more well-developed manner if I have anything to say about it.
EDIT: Aaaaand, there are some examples of people not doing that empathy particularly well. [h'/t Improved Initiative]