Hoo boy.
And no, as far as I know, people use them for their intended purposes. Probably because I think the teachers rent them out. Not sure though.
I mean, people have thought about it (Some much more quickly then others. I didn't make the connection of Soundproofed rooms=Sex at school, and didn't even think of it, but a friend of a friend did...)
But those rooms are amazing! You can barely hear anything in there! I mean, if a drum set fell on the floor, you'd hear a dull ringing, but that's about it. Apparently they're a godsend for people in my school practicing for music competitions and such.