The bisexual menace revisited: or, shaking up social categories is hard to do

What is bisexuality? Is it an identity that a person holds, something one is? Is it a behavior, something one does? Is it stable? Or does it shift and float and change? Is bisexuality distinct from heterosexuality and homosexuality? Is it a little bit of both, or neither? Does bisexuality have the potential to end sexual categories altogether, or does it constitute a new, third category?