If you haven't already seen Seth Godin's blog entry on it and checked out Brand Tags, take a look now.
A brand is not just a name or a logo. It's a set of associations imprinted in the mind of a customer. At the Brand Tags site, you can say what various popular brands mean to you. You can also see what words other people have associated with brand names. Best of all, you can view a set of these "brand tags" and guess the associated brand name.