I actually started a thread here in GLBT about it once - last year, I think it was.
As a follow up to that thread (since I was unable to find it, even after doing a search), my friend later explained to me that even though he works with straight people (as most of us do) who claim to be accepting of gay people, "I'm not going to come out to them because they really are NOT accepting or understanding; they think they are, but they just aren't."
Now THAT I agree with to some extent, more or less - but yes, there is truth in that. And when you come from a society that is deeply homophobic, you are probably more likely, as a gay person, to subscribe to the notion that gay people can be "too gay" - "too gay" for what is the question in my mind - To get dates? No. To have friends? No. To be attractive? No.
I think when people say some gay people are "too gay", what they are really saying is 'I wish I could be as openly gay as they are, but the social pressure to which I'm subjected demanding a certain stereotypical gender conformity is much greater.'