I've noticed it quite a bit, although the kinky community seems to be the most accepting (That I've personally seen) and the swinger community seems to be the least accepting from what I've heard. There seems to be a stigma in society that it's the penis that matters, and bi-men get labeled as gay, even if they're into both men and women. It's not cool.

I spent a while poking around (and by that I mean, I spent a few days' worth of free time inhaling several months' worth of discussions) on swingers' forums when I was in a relationship with a bi guy. I really got the impression that swingers weren't terribly accepting at all. I had started off with curiosity (because hey, informed consenting sex with lots of variety while maintaining a loving relationship as a priority, great right?), but wound up pretty unnerved by their lack of acceptance as a community for many kinks outside their own. The general rule (of course I'm sure there are exceptions, I'm just explaining the vibe I got from the "cumulative average" of the sites I read), but it really did seem that a lot of the men would feel threatened by being in the presence of a bi male.

Made me kind of sad. I'm not really in the swinger community's age range, though, and perhaps there's room for people my age to come up with a more inclusive community.

I'm pretty sure that bisexuality in general is more embraced in females than in males. There's probably a lot of reasons for it, but it definitely is unfortunate. Hopefully that will start to change.