This is a great little book, full of funky tricks and tips for improving, amongst other things, your mental arithmetic, memory, ability to brainstorm effectively and so on.
The hacks themselves are split neatly into eight sections: Memory, information processing, creativity, math, decision making, communication, clarity, and 'mental fitness'
Some of the hacks in the book are pretty intense, requiring a fair amount of legwork (or should that be brainwork?) to get them up and running. Some of the memory systems for example would clearly need you to remember the system before you could remember other things!
I loved the way that the hacks are set out - starting out with what the hack will achieve, how it would work 'in action', then applying it so that you can see how it would work 'in real life'
My favourite section was the Creativity section, with some great ideas and tips for getting the old grey matter ticking along. As with every O'Reilly book I've read, the author's style is friendly, clear and informative, not to mention funny.
You may not use all the hacks in this book, but I'll bet you a dollar you come out of it wanting to try more than a few. Top stuff.