Yeah, having a Darwin build of the docker client is useful but it's only the first step in our OSX support, we need to add a few more things before "zero to docker" feels really seamless on a Mac. Specifically we need to bundle a lightweight VM [1], automate a headless virtualbox/vmware setup [2], wrap it all in a DMG and homebrew recipe, then do it all as part of docker's release flow. When that's ready we'll overhaul the docs.
[2] A possible candidate is http://github.com/noplay/docker-osx if they change a few things, namely expose the native binary instead of wrapping it, and remove the dependency on vagrant which is overkill for a hardcoded image. The boot2docker folks are also working on something similar, maybe they can collaborate.
[1] Probably with the awesome http://github.com/steeve/boot2docker
[2] A possible candidate is http://github.com/noplay/docker-osx if they change a few things, namely expose the native binary instead of wrapping it, and remove the dependency on vagrant which is overkill for a hardcoded image. The boot2docker folks are also working on something similar, maybe they can collaborate.