I played around with the sign-up form because I'm designing something similar at the moment. Once I get a "username not valid" error, I can't re-enable the subm

I played around with the sign-up form because I'm designing something similar at the moment. Once I get a "username not valid" error, I can't re-enable the submit-button anymore. You might want to fix that. Also I don't think that the username was already in use, because I entered a random email. Probably a validation error. To say something positive: I like that the headline changes the last word periodically. That caught my attention.