It's amazing actually how many companies spend large amounts of money on special routers or software or whatever to mess with p2p traffic - considering there is a module for iptables which allows any linux router to mess with p2p traffic for free with very little extra configuration needed (a single rule to drop all matching traffic, or ideally a rule to mark the packets for QoS to give them a lower priority to only use idle bandwidth rather than completely blocking it) - or of course you can use a couple of rules for bandwidth usage of connections rather than specifically matching p2p protocols