I admit that I've been caught up in the Facebook hype. Marc Andressen's post on their API has caught a lot of attention, and for anyone building web stuff, a ready audience of 25 million active users is hard to ignore.
So I went to Amazon and bought the only book I could find about Facebook - Inside Facebook. It's written by an engineer who worked there for all of 1 year. He was a bit of an outsider being the only guy over 30 for a long time and not being part of founder Zuckerberg's Harvard mafia.
The book really doesn't have a great deal of info in it, it's short, full of links, and better consumed as a PDF. It's more like a series of blog entries.
About 20% of the book is actually about Facebook, covering the names / titles of the early employees, a bit of the vision, and some anecdotes / factoids. For example, Zuckerberg has two business cards, one with the title: CEO and another that says I'm the CEO... bitch. Zuck also doesn't like coffee much.
If you want to know who the braintrust is at Facebook, you'll at least learn their names: Dustin Moskovitz, DeAngelo, Jeff Rothschild, Matt Cohler, etc.
Overall, the book is underwhelming, but if you are thinking of interviewing at Facebook, or partnering with them, it's definitely worth the $10 bucks and 40 minutes it takes to read.