Consutlant Bilal Siddiqui wrote a series of articles at IBM developerWorks around Acegi. Definitely worth a read if you're trying to understand Acegi. Our reference guide is good, but it's a bit over the top for most folks.
The first article was released in March 2007. The third part was released on September 25 2007. I've fallen behind on my feed reading a bit :P