I don't think people should be allowed to make an app to run on a p2p network. You realise the main source of law suits involving copyright infringement and music/film downloads is down to p2p networks?
For someone to say that there are legal things on p2p is laughable.
I wouldn't condone anyone made a p2p application for the iPhone for this very reason.
Regardless of this, torrentula (or w/e its called lol) can be used for legal purposes as you will find many sites that use torrents as a means for distributing things such as Operating systems.
Rant over, but sorry i hope they never make limewire for iPhone!