Updated to include information about WordPress 3.8, complete with new screenshots and new plugin recommendations is my most popular book, WordPress Multisite 101.
What can I say about it that you don’t already know? Oh I know! I’ll quote Nacin! When he was asked for advice about Multisite, he replied “Basically read everything @Ipstenu has written (including when she suggests to not use it).”
— Andrew Nacin (@nacin) December 20, 2013
See? Can’t get more awesome than that, can I?