What topics are covered? As with the Manual all the basics are there. Attack position, braking, cornering, flow, jumps, drops, pumping, bike setup, the list goes on. Certainly everything I want to know is clearly explained with a bunch of diagrams/photos. I had several eureka moments when reading MMBS. "Oh right, so that's how you're supposed to do it!", "Ahhh so that's why pumping makes you faster!" If you had been in a room with me you would have seen a lightbulb appear above my head, on more than one occasion. In addition, at the end of each chapter is a troubleshooting section. Common problems and the solutions. Really really useful stuff.
There's something else I like about MMBS. Don't be fooled into thinking it's just a dry text book, it has personality, by the bucket load. Several pages made me smile. Here are a few of my favourite quotes:
On exploring the limits of your cockpit:
"Push back until your arms straighten or your bum gets the knobby treatment."
On braking during a corner:
"If a unicorn suddenly appears if your corner, first straighten out; then brake hard. If you've been practicing your braking skills, you'll be under control before you strike the magical beast."
On doing a wheelie:
"Explosively push your torso upward and backward with your arms. At the same time, uncork a powerful pedal stroke. If you are nice to puppies your front wheel will pop up."
To summarise; great explanations, lots of diagrams, buy it now.