Juju person here. Docker would be a nice enhancement for Juju. Currently we use LXC in our older version (.7 in python) for a local provider to deploy containers on your local laptop. The idea is being thrown around to instead use Docker containers in _every_ provider like EC2 and OpenStack. This would enable you to just move stuff around transparently, which is awesome.

The Juju team is keeping a close eye on Docker and it'll likely (but I can't promise) be in 13.10.