Good talk. Interesting that Facebook uses MySQL mostly as a key-value store to represent directed graphs. There was a discussion recently about how FriendFeed does essentially the same thing. <a href="http://bret.appspot.com/entry/how-friendfeed-uses-mysql" rel="nofollow">http://bret.appspot.com/entry/how-friendfeed-uses-mysql</a>. I'd like to see a bit more about how they implemented this.