Probably not too often. Personally I think that'd be pretty weird, but then again if you really like a guy, the name shouldn't get in the way.
There's a gay couple living in our house, they're both called Bernd, and claim to be friends with a couple of Thomas's. I guess if you have a common name it's not unusual. The person I have a crush on has her birthday on the same day as me, how probable is that?
I've never had it happen to me, and I don't know anyone personally it has happened to. My dad has had three boyfriends named Stephen.