This happened to me the other day as well when I was moving from the beta to tests-passed channel. Very “buggy” at least appears that way, and creates quite a bit of downtime when you have to make 2 or 3 attempts at it. Perhaps the messages could be more verbose so people know things are happening in the background?
Update: Was just upgrading to 14.04 LTS and the same thing happened as described above. Had just rebooted after upgrading the OS, and 20 minutes into the bootstrap process, it was hanging at * Background saving terminated with success for 10+ minutes. I rebooted, and tried to bootstrap again. This time it hung several minutes after updating /etc/nginx/conf.d/discourse.conf with SSL information. Another reboot and re-bootstrap, seemed to work, and only took a couple minutes. However when trying to start the app, I got:
2014/10/08 10:49:07 Error response from daemon: Cannot start container 45892ae9d79e85a30ec1b43d597aabc334257bced330972f3477b20a29f9c767: Cannot find child for /app
Following https://meta.discourse.org/t/error-response-from-daemon-cannot-start-container-hash-cannot-find-child-for-app/20685 resolved that, and I’m finally back in business after an hour. 
2GB box at DO.