Personally, the only problem with myspace I've had is finding my students pages & seeing VERY inappropriate pictures posted... I mean, if I can find them, who knows who else is viewing their pages...?
But yes... the students who worry tend to post inappropriate comments, pictures, etc.... and someone always manages to take offense... to the point of taking general comments as though they are specifically aimed.
I enjoy maintaining my own page, and hope my friends enjoy it, too.