Wow guys! This is great iniciative. Congratulations!!
I'm looking forward to buy a couple of shirts, I've already choose 2 motifs.
Just a little suggestion: to add a "Register" user option in "My Account" drop-down menu or anywhere of easy access.
Also in "Login" you can add a "aren't you registered yet?" option alongside "Lost password?" or something like that.
thanks!! 
Thanks Peche actually we wanted to make it super easy for everyone so registering is actually optional, you can shop without doing that.
The "already registered" option shows up when you go though checkout so you don't have to re-type your shipping address again.
If you are logged out and want to login, you just click either of the options in the my account dropdown menu, there will be a prompt for your username and pwd.