That isn't official documentation as far as I can tell, though. I don't think I should need to read 5 chapters into a separate book for something so seemingly fundamental.
IMO, this is important enough information that it should be mentioned from the start, but it isn't in the tutorial[1], nor can I find it in the FAQ[2].
You're right, it's not official documentation, but it was the first thing I read when I decided to start learning Mongo. I've also seen 10gen hand out hard copies at meetups in NYC. Anecdotal, I know, but maybe helpful to someone.