Applied Docker: Continuous Integration

I just started playing with docker and it is very cool, but I am not sold on complete isolation of every service in a stack.

I've taken to building my containers using packer & ansible, with docker acting as something between git and an lxc client.

If you run your tests against live instances do you deploy the exact same container? How do you control environmental or configuration drift?

I'd be interested in seeing a CI tool on top of docker :)