Awesome. Will definitely be playing with this. One of my biggest frustrations with getting docker on my pi has been the lack of support for arm builds and having to rebuild every image needed (which kind of defeats the purpose of docker hub).
It's supposed to be an email verification step after which your selected username/password should work. We'll check if we can improve the messaging to make it clearer.
http://marina.readthedocs.io/en/latest/tutorial/quickstart.h...
Helpful screenshots illustrate the whole process :)