There's https://github.com/codekitchen/dinghy if you want to mount the Mac host volumes inside boot2docker via NFS. We have a Vagrantfile that does this, but dinghy packages it all up nicely.

At the end of the day though, Docker as a development environment is really bad on OS X until a VM vendor fixes file share performance. I really wish Docker would make it a priority to have decent Mac support.