A version of Django's UserCreationForm that uses email instead of username, with some nifty features. (Maybe not super robust yet, in terms of concurrency...)

forms.py

import re
from django import forms
from django.contrib.auth.models import User
from django.contrib.auth.forms import UserCreationForm

class UniqueUserEmailField(forms.EmailField):
    """
    An EmailField which only is valid if no User has that email.
    """
    def validate(self, value):
        super(forms.EmailField, self).validate(value)
        if Users.objects.filter(email=value).exists():
            raise ValidationError('Email already exists')


class ExtendedUserCreationForm(UserCreationForm):
    """
    Extends the built in UserCreationForm in several ways:
    
    * Adds an email field, which uses the custom UniqueUserEmailField,
      that is, the form does not validate if the email address already exists
      in the User table.
    * The username field is generated based on the email, and isn't visible.
    * first_name and last_name fields are added.
    * Data not saved by the default behavior of UserCreationForm is saved.
    """
    
    username = forms.CharField(required = False, max_length = 30)
    email = UniqueUserEmailField(required = True, label = 'Email address')
    first_name = forms.CharField(required = True, max_length = 30)
    last_name = forms.CharField(required = True, max_length = 30)
    
    def __init__(self, *args, **kwargs):
        """
        Changes the order of fields, and removes the username field.
        """
        super(UserCreationForm, self).__init__(*args, **kwargs)
        self.fields.keyOrder = ['email', 'first_name', 'last_name',
                                'password1', 'password2']

    def __generate_username(self, email):
        """
        A simple way of deriving a username from an email address.
        Hat tip: http://bit.ly/eIUR5R
        
        >>> User.objects.all().order_by('-id')[0].id
        1
        >>> self.__generate_username("abc@gmail.com")
        abcabc2
        >>> self.__generate_username("hey.what.is.up@hotmail.com")
        heysup3
        """
        # TODO: Something more efficient?
        highest_user_id = User.objects.all().order_by('-id')[0].id
        leading_part_of_email = email.split('@',1)[0]
        leading_part_of_email = re.sub(r'[^a-zA-Z0-9+]', '',
                                       leading_part_of_email)
        truncated_part_of_email = leading_part_of_email[:3] \
                                  + leading_part_of_email[-3:]
        derived_username = truncated_part_of_email + str(highest_user_id+1)
        return derived_username
    
    def clean(self, *args, **kwargs):
        """
        Normal cleanup + username generation.
        """
        cleaned_data = super(UserCreationForm, self).clean(*args, **kwargs)
        if cleaned_data.has_key('email'):
            cleaned_data['username'] = self.__generate_username(
                                                        cleaned_data['email'])
        return cleaned_data
        
    def save(self, commit=True):
        """
        Saves the email, first_name and last_name properties, after the normal
        save behavior is complete.
        """
        user = super(UserCreationForm, self).save(commit)
        if user:
            user.email = self.cleaned_data['email']
            user.first_name = self.cleaned_data['first_name']
            user.last_name = self.cleaned_data['last_name']
            user.set_password(self.cleaned_data['password1'])
            if commit:
                user.save()
        return user