I did once, it was with a long time friend when we were in our last year at univerity. I had never questioned my sexual identity up to that point and even now I wouldn't really identify myself as bisexual. I find other women asthetically pleasing and the fact I grew up in a household with a very conservative mindset made the whole thing feel exciting and naughty, like I was breaking the rules, but I don't feel the same purely sexual attraction to other women that I feel towards men.
That said it was a very eye opening experience and quite enjoyable. I am confident I know what I want from a relationship and that I want a relationship with a man, there is something about the emotional dynamic between a man and a woman that really makes a relationship what is it (I'm only speaking for myself here). That said, being single I wouldn't be oposed to repeating the experience with the right person.
The friend with whom I shared that experience decided a short while afterwards that she was in fact gay and was far happier in herself having discovered that. While nothing else happened between us (obviously) we have remained very close friends and we both regard it as something very special we shared.
Addition - Having read that back to myself and considering how I have never shared any of that before I'm suddenly quite taken aback that I just did