just checked and they do the same thing, so this wont solve any long query problems, but it is cleaner:
In [6]: User.objects.latest('pk')
DEBUG util (0.001) SELECT `auth_user`.`id`, `auth_user`.`password`, `auth_user`.`last_login`, `auth_user`.`is_superuser`, `auth_user`.`username`, `auth_user`.`first_name`, `auth_user`.`last_name`, `auth_user`.`email`, `auth_user`.`is_staff`, `auth_user`.`is_active`, `auth_user`.`date_joined` FROM `auth_user` ORDER BY `auth_user`.`id` DESC LIMIT 1; args=()

In [7]: User.objects.all().order_by('-pk')[0]
DEBUG util (0.000) SELECT `auth_user`.`id`, `auth_user`.`password`, `auth_user`.`last_login`, `auth_user`.`is_superuser`, `auth_user`.`username`, `auth_user`.`first_name`, `auth_user`.`last_name`, `auth_user`.`email`, `auth_user`.`is_staff`, `auth_user`.`is_active`, `auth_user`.`date_joined` FROM `auth_user` ORDER BY `auth_user`.`id` DESC LIMIT 1; args=()