NOTE It would be a nice addition if you could check whether a given user name
already existed before the user tried to submit the form. You can use the techniques
from previous chapters to accomplish this easily. For example, you could
use a page method at the server to check whether a given name was already
taken. You could then call this page method with some JavaScript as soon as
the user moves away from the User Name field. For a step-by-step guide of this
solution, take a look at this article on my website: http://bit.ly/Ldgr2j.