[nznog] Caching peer-to-peer traffic: a done thing?

I'm updating my labnotes for my network management paper regarding the use of proxy caches, and previously I have pointed to the possibility of caching peer-to-peer traffic as shown in the paper Deconstructing the Kazaa Network http://portal.acm.org/citation.cfm?coll=GUIDE&dl=GUIDE&id=837393 I would like to know whether or not caching of peer-to-peer is something that ISPs actually do today, and if not why not. I imagine there are probably some interesting legal interactions, but I'm eager to find out how industry is moving in this field. -- Cameron Kerr Teaching Fellow, Computer Science, University of Otago