here's what they're doing, as I wrote last year:

http://machinist.salon.com/blog/2007/10/19/comcast/

To detect peer-to-peer communication, Comcast inspects packets -- the smallest meaningful bit of information on the Internet -- as they cross the network boundary. If Comcast determines that there are too many peer-to-peer users within its network sending files to people outside the network, it begins to interrupt the connections between Comcast users and those beyond Comcast.

To interrupt these communications, Comcast appears to be using technology made by a network management company called Sandvine. What's remarkable is how Sandvine manages to disrupt peer-to-peer traffic.

As Topolski describes it, Sandvine's system sends a "forged" packet to each of the two computers engaged in a peer-to-peer transfer -- the forged packet looks like it came from the other person's computer, and it basically tells each machine that the other is unavailable, ending the transfer.

The AP describes this marvelously: "Each PC gets a message invisible to the user that looks like it comes from the other computer, telling it to stop communicating. But neither message originated from the other computer -- it comes from Comcast. If it were a telephone conversation, it would be like the operator breaking into the conversation, telling each talker in the voice of the other: 'Sorry, I have to hang up. Goodbye.'"

As an earlier poster mentioned, there are ways to customize their routers right now. However, managing the quality of service (read: traffic) by adding in policies for every subscriber is usually a pain to configure and a nightmare to monitor. It's much easier to send out a new global firewall rule that just blocks a particular port (and I assume that's what they're doing? not actually analyzing all traffic?).

"Why a law when there has been no harm?" Conservatives use that argument a lot when arguing against Network Neutrality. Well now there has been harm. Thanks for the excuse Comcast. Lets get that law passed.

They could charge line hogs more - to the point of subsidizing service for the rest of us.

Or they could configure their routers, using mechanisms available today, to give the hog traffic the lowest possible priority. Promoting mail (yummy spam!), web access, VoIP, ftp, and all the other uses above the PTP.

Slowing down the hogs to provide for all other use types to traverse the net first would meet their stated objectives.