For me, no way. I am a BIG sucker for good jeans on guys! To their knees? nooo! If it's a little bit below their waist.. lets say around their ass or something.. sure! that's fine. But going too low is a total turn off for me. But then again, some girls love it. This is just a one girl opinion :S
Oh gawd no. I think that is so unattractive and disgusting. What makes guys think that we want to see their fruit of the looms? I mean honestly! I love when guys dress modestly with pants at waist height =] I'm glad you asked.
If the majority of guys are doing it, do the complete opposite. You'll get more attention because you'll stand out from the crowd.
Jeans rolled up to their knees? Gay
Jean's pulled down to their knees? Gay
I wear jeans that FIT, and I find a get a lot more compliments on how nice my jeans are (I wear brand name stuff) than how I am wearing them. If you wanna be a thug however, that's your choice to make.