User a list of when all users joined.

gistfile1.py

from datetime import datetime


#########################################
# Set up the django environment
#########################################
from django.core.management import setup_environ

import settings
setup_environ(settings)

from django.contrib.auth.models import User


#########################################
# Set the granularity of the report
#########################################
GRANULARITIES = {
    'y': (lambda x: [x.year, 1, 1],
          '%Y'),
    'm': (lambda x: [x.year, x.month, 1],
          '%Y-%m'),
    'd': (lambda x: [x.year, x.month, x.day],
          '%Y-%m-%d'),
    'H': (lambda x: [x.year, x.month, x.day, x.hour],
          '%Y-%m-%d %H:%M'),
    'M': (lambda x: [x.year, x.month, x.day, x.hour, x.minute],
          '%Y-%m-%d %H:%M'),
}


def get_granulatity_options(granularity):
    return GRANULARITIES[granularity]


def group_users_by_join_date(date_fields):
    grouped_users = {}
    for u in User.objects.all().values_list('date_joined'):
        join_date = datetime(*date_fields(u[0]))
        grouped_users.setdefault(join_date, 0)
        grouped_users[join_date] += 1
    return grouped_users


def convert_to_list(grouped_users, date_format):
    grouped_users_keys = grouped_users.keys()
    grouped_users_keys.sort()
    return ["%s: %d" % (x.strftime(date_format), grouped_users[x])
                                                for x in grouped_users_keys]


if __name__ == "__main__":
    from sys import argv
    granularity = 'y' if len(argv) == 1 else argv[1]
    date_fields, date_format = get_granulatity_options(granularity)
    grouped_users = group_users_by_join_date(date_fields)
    total_user_count = sum(grouped_users.values())
    for grouping in convert_to_list(grouped_users, date_format):
        print grouping
    print 'Total Users: %d' % total_user_count

I may extend to allow for the passing of a django settings file path that can be imported instead of presuming it's on the path as settings.py