I did some reporting on Facebook and Xanga earlier this year and spoke with Robin Raskin, a writer and tech consultant, who has a site called Raising Digital Kids.
Her advice about dealing with the rise of social networking and how much information kids can put out there about themselves? Do drive bys. She says it make sense to check out your child's site--and the sites of their friends. This generation's notion of privacy is basically non existant.
It sounds like a lot of the responsibility is up to parents. Beyond not allowing teenagers to use their school emails or to use computers at school to sign in, there isn't much a school can do about monitoring kids. Of course, once kids write something that violates a code of conduct, schools can expel them.