Django Registration without username
A simple adaptation of RegistrationFormUniqueEmail from django-registration http://code.google.com/p/django-registration to allow users to register without using a username. This works great with the code from this comment: http://www.djangosnippets.org/snippets/74/#c195 to allow users to completely eliminate the need for a username.
The solution above will only work the first time a duplicate is found. For example, if firstname.lastname@example.org registers, his username will be "joe". If email@example.com tries to register, it will find "joe" and will get a count of 1 and username will be "joe2". However, if firstname.lastname@example.org tries to register, the local part will be "joe". It will still get a count of 1 and it will try to set username to joe2 and your application will get an error. This is because filter is "username=joe" (thus, not finding "joe2"). A better solution, and one that will prevent this error is:
c = User.objects.filter(username__startswith=localpart).count()