I ran across this today when i was looking for actionscript help for making a slideshow with buttons. (i've forgotten how to do it and if anyone could help me PLEASE HELP) but besides the point I ran across this smart little article in smashing magazine about brand books and why they are important.
It's always nice to see what other people are doing but its even better when you find something pretty clever. Here is an article in which Christopher Doyl did a brand guide on himself. I'm tempted to make my own. I have some pretty good ideas about what I might do.