Blogger Michael Arrington seems to have already performed a helpful proof-of-concept by adding Mark Zuckerberg to a group supposedly representing NAMBLA, the NorthAmerican Man-Boy LoveAssociation.
At launch, there were some concerns about privacy as well as complaints from users about not wanting to be added to certain groups ( Mark Zuckerberg himself was added to the NorthAmerican Man-Boy LoveAssociation, but quickly left the group).