Archiving Policy?

I am trying to find out what other companies do about archiving user files. We are not currenlty archiving anything. Everything is backed up on a rotating schedule, but we only have the past two weeks to retrieve from. We are investigating the idea of archiving all incoming and outgoing e-mail, but are uncertain whether we should also archive user files in the "My Documents" Folder and in any shared folders. Please share your strategies.