I like the anon comment that they should not re-invent the wheel so much. That gave me a chuckle, I'll just use my off the shelf distributed web app deployment software that runs on thousands of machines ... oh snap!
From the comments at Quora, this presentation is great (and dated this month):<p><a href="http://www.infoq.com/presentations/Infrastructure-at-Facebook" rel="nofollow">http://www.infoq.com/presentations/Infrastructure-at-Faceboo...</a>