This addon displays the current number of users waiting approval for membership in the moderator bar. If the entry in the moderator bar is clicked, it takes you to the New Users Awaiting Approval section of the Administration Control Panel.
ATM this adds maximal 2 global queries (depending if the admin permissions are already cached or not) to each page load for admins only, but i'm planning to cache this in the next release It adds 0 queries to your public pages. The value is being cached and rebuild after the user registration or user approval
If you want to support me, and the development of future add-ons, you can donate any value to my paypal account