There are slides from the IETF P2PI workshop from Comcast on both their problem and the traffic shaping approach they are looking at (effectively a tuned user-fairness mechanism).
Part of Comcast's problem is the DOCSIS head doesn't get to see layer3 information when making access, so they can't do something like "make sure YOUR VoIP works if you are being throttled", but it CAN at least make sure that other users are not affected. http://www.funchords.com/p2pi/slides/02-Comcast-IETF-P2Pi.pdf
