We're almost there with the open-sourcing, I'm pleased to say.
Sadly this process has taken far longer than we hoped because the codebase, which was started about 6 years ago and which was not started with open-sourcing in mind, ended up with a lot of things like embedded passwords, deploy scripts, people's names, API keys, etc. There's been a mammoth effort to deal with that. The entire deployment system has had to be rewritten, for instance, and that done while trying to keep a very busy production system running that also hosts a pile of third-party sites without downtime.
http://www.cyclestreets.net/blog/2012/01/09/open-sourcing-ef...
And, tantalisingly, the codebase is on github - it's just that the main bit - the routing engine - is not open:
https://github.com/cyclestreets