Taking a break from Custom XML for a moment. more posts on the topic are imminent.
Jennifer Michelstein announced the Office Ribbon Hero today, a fun thing you can install with Office 2007 or the 2010 beta to test your depth of usage of Office.
The challenge, of course, is for you to beat me. :) Good luck with that.
Really, this is a tool that will help you become more proficient in using some of the capability in Office applications. And let's face it, there's nothing that says "I'm smarter than you" like being the best on your block at using Excel.
You can get it here: http://www.officelabs.com/ribbonhero