One of the really great, although probably overlooked by most users, features of WordPress is that you can store meta data on your users. You probably already know that you can do this for posts, but it’s possible to use the _usermeta table to keep track of custom user settings as well.
A few months ago I redid an ecommerce site of mine and changed from osCommerce to WordPress. One of the bits of information I’m now storing is how many credits the user has available to download templates. It works great but there wasn’t a way to check how many credits they had available without going into phpMyAdmin.
So I went out and wrote my first WordPress plugin. The zUserMetaViewer plugin adds itself as a sub tab under the Users tab and displays a clickable list of users. Clicking on a user’s name will take you to a page where all the meta data for that particular user is displayed.