[Aerdan]

What FRDS said: if there is certain uploadable content that they post that you want to be able to use for publicity use, you're certainly allowed to put that sort of information in a TOS, but even Facebook (as mentioned) took a huge backlash from that. Most importantly, if someone were to post something illegal on there and someone sees it and reports it, that's on your hands now because of the ownership claim.

You may want to consider the route of "XXX is not responsible for any comments, defamation, etc" type of clause to cover yourself legally from lawsuits. You never know who may try it, and the trickiness of legal wording can bite you.