Gilbert strings together a variety of studies to help explain one of the greatest mysteries of our time: how 'happiness' works. The book is chocked so full of useful information that it has become one of my best reads in a long time.
Interesting tidbit: humans are really bad predictors at what will make them happy.
Interesting tidbit 2: Most people would drive across town to save $100 on a $200 stereo but would not drive across town to save $100 on a $20,000 car. Even though they save the same amount of money.