Great and useful, and not just for WordPress MU

You should make it clear this works as well for regular WordPress.

Use case scenario where your plugin fixed a problem for me:

To test WooCommerce with PayPal, we use PayPal’s sandbox, which creates by default two buyer+facilitator test email accounts, derived from your actual address.

These emails do not exist, but you have to make test payments with the buyer. Your plugin was great to create a test user account in the dashboard, with fictive email. Click on ‘don’t notify the user by email’ and set its password. Otherwise, with no password, you would not be able to use this account.