This is weird: the next version of µTorrent, currently in beta, uses an updated version of the BitTorrent protocol that decreases your speed (usually uploads) when it detects network congestion. Will it slow downloads? Not necessarily…apparently.
"uTP measures the time a packet takes to get sent from peer A to peer B, so in theory uTP will detect congestion anywhere on that path, although in practice the congestion most often happens somewhere on the first-mile uplink connection."
So won't that effect seeding—the very concept torrenting is based on? What if you're throttling yourself while everyone else is downloading like mad with a non-uTP client? TorrentFreak says that beta testers haven't reported any significant issues, and suggests that a more efficient use of the network may actually boost download speeds. uTorrent has a massive user base, and if all those users switched over, maybe that could happen.
If you're with an ISP who slows you down when you use too much bandwidth (like Comcast), or any provider that slows down when it's congested, uTP could actually be a very positive thing.