Not able to answer your question since I'm a guy, LittleDevil, but this question has always intrigued me.
I believe that there are, ahem, one or two men out there who enjoy the thought/idea/image of women together, yet as a reversed scenario it doesn't seem to be as popular (women getting off on men together).
This is a bit of a shame. I lamely describe myself as bi-curious but have never had an experience with another man, although I would like to try it. However I'm essentially straight and the enjoyment would mostly come from doing something that I haven't tried before since I don't really fancy men. But it would be a lot more enjoyable if there was a woman present who I knew was getting off on the sight.
Anyone have any theories as to why women don't enjoy M/M as much as men enjoy F/F? Is it just as simple that female bodies look nicer than male ones?
I read somewhere that when a woman likes to watch gay men go at it, it's because she truly loves the male body, and in her fantasy there is no room or need for a woman.
I personally would like to have a cock sometimes - when I'm fingering my husband's ass, feeling it's smooth slickness, I just want to fuck him - but with a toy, I can't FEEL it, you know?