Avoid new user notification on user_save
I can't find a way to do that. user_save doesn't take such an argument. I believe you have two options.


Emulate the user_register_submit() call by passing your data in as a form instead, this is preferably done with drupal_form_submit(). It just so happens that the example deals with user-registration.
Just kill outgoing e-mails while you import your users.