Peer to peer applications are changing it seems. uTorrent is running experiments that may see it shift a lot of data from TCP to UDP. In the short term this would benefit some torrent users since providers that have simply rate limited the TCP ports used by BitTorrent will have to play catch up, and UDP by its connectionless nature may prove to be harder to traffic manage, but given providers can identify UDP gaming traffic it will only be a matter of time before any limits kick back in.
The Register has an article by Richard Bennett that tells us that Gamers, VoIP users and video conference users need to beware. Now if a provider has allocated just 20% of its available bandwidth to UDP traffic at peak times, and P2P starts to shift into this area, then yes packet loss may rise and jitter, when the packets arrive with variable delay, will increase. Simon Morris who is a BitTorrent Product Manager has countered The Register's article on utorrent.com.
uTP is our UDP-based implementation of the BitTorrent protocol. Normally BitTorrent is implemented on top of TCP which is the standard congestion control mechanism for the internet. It so happens that the congestion control mechanism inside TCP is quite crude and problematic. It only detects congestion on the internet once “packet loss” has occurred – i.e. once the user has lost data and (probably) noticed there is a problem. The problems of TCP are fairly well known in technical circles, but it doesn’t get fixed as TCP is one of those protocols that is implemented in every OS, client and server, on the internet. Co-ordinating a giant upgrade is a very long process.
Because BitTorrent publishes the world’s most popular BitTorrent clients AND because these clients are talking mostly to each other (not to web servers), then we have an opportunity to detect end-to-end congestion and implement a protocol that can detect problems very quickly and throttle back accordingly so that BitTorrent doesn’t slow down the internet connection and Gamers and VOIP users don’t notice any problems. This is our objective.Simon Morris BitTorrent Product Manager
So it seems they are claiming that the new uTP layer they've added will throttle the UDP packets back when congestion is seen, but it is not clear whether we are talking congestion on an individuals connection, or congestion at any point between two peers? If peer to peer is trying to behave better and be more traffic friendly then that is perhaps to be welcomed, but gamers are often some of the first to notice problems, and any packet loss or jitter that this causes can ruin a game.