I'm reading and testing a bit about this new tool (Docker), and after some time I discovered some tips that I wanted to share with you guys.
1 - Check out other containers filesystems
Maybe for what you plan on installing inside a container, the default filesystem that Docker uses (AUFS), ins't the best choice. A pretty good example is a MySQL DB image, that has a problem already documented. But don't be alarmed, there is a workaround for this! You just need to change your Docker filesystem to Device Mapper.
2 - Debugging Containers With Nsenter
If you want to debug your containers, and don't feel very well installing a SSHD inside each container just to navigate inside it, then you should use Nsenter. This allow you to get a prompt inside your container that has a process initialized, and it doesn't hurt the Docker principle (one concern per container).
You can read more about this in here: If you run SSHD in your Docker containers, you're doing it wrong!
3 - Test things with Vagrant!
Had problem installing Docker in your machine? Or maybe you just want to test this new tool in a clean environment? That's easy, since the guys from Phusion created a base Vagrant image that has it's a kernel ready to install docker.
So all you have to do is
$ vagrant init phusion/ubuntu-12.04-amd64
And you'll have a Vagrantfile ready to go.
More info on this in here: Docker-friendly Vagrant base boxes
That's all, and have fun playing with Docker!