Don't see any reason why not. If the content is illegal, it is the responsibility of the host to remove them. Rapidshare and Megaupload is pretty good at handling complaints.
If you post the links to infringing material or encourage users to do so, then you can get in trouble in the US. If your users are the ones posting the links, then you should be fine.
Well, if is infringent copyright material you shouldn't in anyway let them put links. If its home made material or nothing illegal, let them
In US they will try to fuck u up, but host ur site somewhere else and u are fine. Thats what I am doing. FUCK USA