P.S.: Curtis Villamizar had another interesting approach which involved pushing content far afield to machines with the same transport-layer (IP) addresses, relying upon closest-exit routing to connect one to the topologically-closest replication machine. Unfortunately, while this could be really cool for NSPs to offload stuff towards peering points (public or private), it also has some poor scaling properties and is uncomfortably reliant upon the stability of routing.
If he's done any more thinking about the idea, I'd love to hear about it though.
I don't know about Curtis, but others have solved this problem (in theory) recently. We at Net Access have figured out a way (we believe) to get around the stability-of-routing issue for already-established TCP sessions in the above approach (multiple machines with the same IP externally, plus an internally different IP, each running gated to announce their /32(s) to your IGP) - hint: a question I asked on NANOG a few days back - And Alec Peterson (now of Erols) has figured out an even arguably slicker way to do it. I'll see if Merit wants to have Alec and I do a presentation on the methods @ NANOG. We should be able to implement our various solutions by then... Avi