I came across this tidbit the other day for using Ubuntu cloud images with Docker, and I thought that Ubuntu Core might be a better starting point for your own base containers:

curl -O http://cdimage.ubuntu.com/ubuntu-core/precise/daily/current/precise-core-amd64.tar.gz
cat precise-core-amd64.tar.gz | sudo docker import - precise-core

nb: Ubuntu Core is very minimal – be prepared to install just about everything you’re going to need.