I have refused it, and I would probably refuse it again. I'm too old fashioned...
But I can add something to the topic. Here's a dialog with some years on it between me and a friend, over the cell phone... let's call him "Marco", and the female friend, "Telma":
L.: Hi, Marco. Guess what. I just been with Telma.
M.:Yeah? How is she?
L.: With crazy ideas. Dude, have you ever thought about doing a menage a trois? She wants one.
M.: (with lust in his voice)Really?? Who's her female friend?
L.: (laughing) It's me. She wants me into the mix.
M.: (laughing too) WHAT?!? No way!
L.: (Still laughing) Way.
M.: Man... if it was with another female friend I might go for it, but with a guy.
L.: Yeah, I know. Who's going to break her the bad news?
M.: You do it. Man... damitt, have you imagine, being with a girl and passing your hand over her *** and realising its the other guys ***??!! AArghhhh....
L.: (laughing hysterically) Yeah, man. No way!!
(the conversation got a bit more leud from here)
Curiously, I've only met female bisexuals so far. Oh, and the occasional lesbian. I wonder if that means that women do "come out of the closet" more openly than man? Hmm...
Edited for profanity.
-IC