i have a few times.
the one chick was just a total raging psycho though. complete nut case. i didn't want a relationship with her, just an occasional fuck buddy. she wasn't having that...one week she was begging for a relationship, the next we were strictly friends, the next week we were "friends with benefits" again. she had some serious insecurity problems and i guess i wasn't helping matters much because i just didn't want a relationship with a chick that had a few loose cannons upstairs. go figure.
she was kinda cool when she wasn't being psycho though, i'll give her that.