Comcast has been messing with my Bittorrent traffic for a few months now. A fix? If you're using Azureus you can turn on transport encryption and require all connected peers to do the same. Everything will be somewhat back to normal... your speed will dip a bit due to having to only use other clients using encrypted transport.

In fact, your overall speed will probably be slower, due to the fact that Comcast only mucks with your uploading. Leeches won't have any problems with Comcast's policies, but those of us who try to keep up a good share ratio have to use the encryption.