Never really thought about it too much. I'm not particularly attracted to men, I just like the sex. I've only ever had meaningful relationships with women and couldn't imaging myself, for example, living as a couple with a man. For me, sex is just sex with a man, but it can be a lot more than sex with a woman. I guess that makes me not bisexual.
There is also the practical side to all of this. In Montreal, it's just a lot easier to get quick, free, anonymous sex from men than it is from women. No dinner, no movies, no phone calls, just one or two beers. And nothing to deal with afterwards. It's Kleenex, you shoot your wad and throw it out.