My parents don't really know a lot of my friends. They do now that I used to work with them though, and they know one of them.
I've never heard them say anything negative about them, but I think it's because I have good judgment... Then again, they don't know I go out there to drink... sometimes, I usually just go there to hang out, and someone would happen to have left some beer there, and everyone raids it.
My family is too trustworthy, They'd leave me home alone with my girlfriend (she's my ex now, and I realize she was a HUGE mistake), and well... We never had sex, but we still went pretty far (She was more of a friend with benefits...)
My mother fusses when I bring girls back, even if they are just friends, she will go into cliche' mother meets possible future wife mode and start asking loads of stupid questions, despite the fact I'm 17.
My mom was the same way... that's why I'd never bring her to my place until we were serious or if it was just a group of friends. I'm 20 now, and I bet if I did bring a girl home (g/f or normal friend) she'd probably still freak like that... I think all moms do it.