On any site that accepts user contributions, a certain amount of copyrighted material ends up getting posted. Quotes used without full attribution are not uncommon, and reuse of copyrighted images is widespread.
In the context of US copyright law, what are the possible ramifications of either intentionally removing or not removing content that you suspect violates somebody's copyright? I understand that the DMCA provides safe harbor provisions if you remove content when a DMCA takedown is filed, but assuming that the copyright holder hasn't notified you, what could go wrong if you either do or don't remove material that might be infringing?