There was a while when I thought I might be. I appreciate attractive qualities in men, have made out with some, and wouldn't even be opposed to being in certain sexual situations with certain men.
I'm primarily attracted to women. More than that, even, I don't see myself ever actively seeking out a gay relationship be it sexual or emotional. And that's where I place the distinction. I'm all for non-heteronormative behavior and experimentation, and I'm definitely not textbook straight, but I don't self-identify as bisexual because I'd never actually desire to be with a man in any serious capacity.
My girlfriend, on the other hand, is very distinctly bisexual. Being raised in a highly liberal environment by a single mother, I'm a male pro-queer, non-heteronormative, feminist...thing. I'll say this, life is never dull in terms of hot button issues for me and mine.