The following opinions are my own, not that of the rest of the ICSI networking group or any funder.
Here are my slides for my 5 minute talk at the IETF Peer to Peer Infrastructure meeting in Boston. In them, I argue that bulk-data P2P is not about cost savings but about cost shifting: moving the cost of providing content from the content provider to the recipient or the recipient's ISP. In particular, this cost shifting is very inefficient, greatly increasing aggregate costs, as ISP transit costs significantly more than content provider transit. This is, I believe, the root of the conflict between bulk data P2P and ISPs.
I also believe that caches are a non-starter, as they are less transport efficient than HTTP caches, are lawsuit bait for illegal content, and don't have a business rationale for the ISP to provide one for legal content.