This is a cool topic!
I guess if it were to come down to "sounding gay"... well , yeah I totally do. But then again, I'm not sure if has anything to do with the fact that I'm gay, or becuase I've been acting for years and years. I've just become more expressive of emotions, and when something exciting happens, i'm EXCITED!
As far as "gay speech" goes, I totally believe in it. While of course not EVERYONE is going to fit in the same category, a lot of peopole do. The entire concept of GAYDAR is based on judging various stereotypes and seeing if a person fits into them. But none of us complain about THAT!
And I also think that sounding gay has a lot to do with how comfortable a person is in a certain situation. I've been known to have my "business voice", which is very even toned and non-excited. This is used during board meetings, and basically whenever the suit and tie come out. But the same thing happens to everyone i think. I've seen some of my gay friends, who many would call straight-acting (another issue I don't really want to get into, because I think it's silly) let out a very camp "hey girl hey" when around friends they're feeling safe with.
So, do I think the gay voice exisits? Yup. Do I think it really matters?? Noooope. But then, half of us would have really bad gaydars without it!