Hacker News Reader

I'm not a lawyer (nor even American) but I believe the most relevant legislation would be the Digital Millennium Copyright Act. In which case, it might be a good idea to formulate a policy similar to the one linked to in the footer of this very website.

It's not a trivial problem, I'd be more worried about users uploading illegal content maliciously. Would definitely require a moderation team depending on the site size...

AFAIK hosting a link could be copyright violation too. All bittorrent sites host links, not real content, yet they are sued and closed.