The new user registration page is clearing the Address's State if there is an error. In my case it was the nickname. Then you get an error for that. It also forgets that you entered a captcha. You should only have to do that successfully once as you have proved you are human. There is also no indication that a Nickname needs to be unique. I would rename that Username, which is thus implied. It is also useful to use AJAX to immediately let the user know that a Username is taken, rather than waiting them to press Submit and get an error. It would also be nice if there was an indication whether the address being entered would be used for billing or shipping, although since I have not yet gone through the purchase process, it may not be an issue.