It can be convenient to prioritize UDP over other traffic for simple QoS at a shared broadband gateway. It catches DNS queries, VoIP, gamers, and most anything else small and sensitive.

In an attempt to avoid ISP filters the P2P users sprawl across all 64k TCP ports. Now the UDP portspace will be covered in P2P crap too. There are lots of major IP protocol numbers left... at least in my copy of /etc/protocols. I wish they'd used a new protocol for this instead of UDP.

But then again, I think we all know the real motivation for this effort is simply to make it more difficult to segregate P2P at the ISP. I don't really care about that; my problem is the collateral damage.