I really wonder how this has managed to slip my attention for so long. With MirrorBrain you can set up a distributed content delivery network. What it does is to redirect users according to GeoIP location detection to the server nearest to them.
MirrorBrain is an open source framework to run a content delivery network using mirror servers. It solves a challenge that many popular open source projects face – a flood of download requests, often magnitudes more than a single site could practically handle.
This could provide an excellent and cost efficient alternative to using services like Amazon’s CloudFront (which is really great, too, as my preliminary tests show).