It should be prosecuted, but in my opinion, I think they should only prosecute people who have uploaded/downloaded a significant amount.
Because let's be honest, I'm sure everybody has downloaded something illegally sometime in their life (I know I'm guilty of doing it), so to do so would be a huge undertaking (though it's definitely already happened).
Meh. Until the law enforcers have better technology and enforcement, I don't think there's really much that can happen.