When your registration form is using a user ID that is the same as their email address, I'm somewhat concerned over spammers using the User name is in use as a means to validate the existence of an email, or if there are other concerns I need to know of for validation sake (for instance, converting CaMeLcAsE to lowercase seems to be the status-quo despite the RFC spec).This question is not about OpenID.
When using email as login name, what precautions should I take for registration?
registration;spam prevention
They can only tell if it's a valid email address if that person has registered with your site, so it all depends on how popular your site gets.I don't think that converting it to camelcase will change anything as they can easily convert to lower case or upper case if necessary.Have you thought of putting a captcha on the site? Google's ReCaptcha is always a good one.UpdateYou could put a flipper around the captcha code (and the code that validates it).See how Flickr and Forrst do it