Just to throw my two cents in:
I'm bisexual, and none of my friends know it. I don't feel comfortable telling my straight or gay friends, and I don't know of any of them being bi as well ( I only know two other bi's period - and they're both only casual acquaintances). All of my friends that I have talked to seem to have the mindset that "bisexuals are confused," or "can't make up their minds." I understand that it can seem a little confusing, since I know a number of gay people that have used the label 'bisexual' as a slightly less jarring transition point to fully gay. However, some people just are sexually attracted to both genders. Its sad, but I just don't feel like I could express that and have it just be known - I really feel as if my friends would just judge it and pass it off as something else. Its really as if the just can't understand.
I don't see why one's sexuality should go beyond just that: sex. Its not a question of love: phileo, eros, or agape, its just a question of eroticism. Frankly, I don't see why any competent person would factor in someone's genitalia into an intangible emotive response to that person. While sex can be the vehicle of eros (romantic love), I don't see why it has to be tied to it solely. Bisexuals don't confuse love and sex - they more clearly define it. Guys and girls get me hard. Deal with it.
Bisexuality is not the "middle ground" on the sexual slide scale - its a third spoke on a wheel of attraction. Once people accept it as a distinct choice and not just and in-between fence straddle, then we can become a cohesive group as accepted as hetero/homo - sexuality.