My parents didn't really mind when I announced I was a lesbian, but then again discussing (and at times, disagreeing) about politics is something that is commonplace in their house. Over last Thanksgiving my girlfriend came home with me, that was nice.
There's ways of checking the temperature of their reaction without actually telling them. If something you're doing or something going on in the news has to do with gay people, talk about it with you parents, see what they think about gay people. It's a good way to gauge how well they'd take it.
Best of luck!
