13May/085
Handeling the dates and the leap year with AJAX and jQuery
Almost all web 2.0 platforms lean toward using an existing e-mail as a form of authorization and authentication. Usually you don't need to use a user name to login or register at a certain site. What they are mostly doing though is the birth date validation. I just encountered a site, which doesn't allow a registration to the people younger than 25 years old. If you went through the registration process and you are older than 25, your re-registration process might be blocked. If you really want to register though and have enough knowledge you can delete your cookies, restart your router (or any other method depending on how you are connected to internet) and register anyway, however probably 90 percent of users doesn't have that knowledge.