Like many, many books, this one is better at describing the problem than it is in proposing solutions. Gilbert contends that our powers of predicting what will make us happy in the future are seriously flawed, and then proposes a simple solution which he correctly predicts that no one will use.
His description of the reasons that our predictive powers are flawed is both fascinating and convincing. However, even in this part (which is the bulk of the book), he makes an unspoken (and apparently unrecognized) assumption: That is, he assumes that "real" happiness or unhappiness is defined by the emotional state that a person feels immediately after, or concurrently with, the event in question.
To use an example: a couple of other reviewers have already mentioned Gilbert's story of a victory in an important college football game. Students predict in advance that they will be ecstatic if their team wins, and a different study suggests that a few months after the fact they will contend that they WERE ecstatic. However, close monitoring of their feelings at the actual time of the victory, or shortly thereafter, suggests that they weren't as happy as they expected to be, or as they later recalled being. On a less trivial topic, he makes the same claim regarding the experience of having and raising children: It isn't as much fun as the parents expect it to be. And while the child-rearing was going on, it wasn't as happy an experience as they later remembered it to be. But Gilbert is ignoring a vital point here: The anticipation of happiness, and the recollection of happiness, ARE happiness! Gilbert writes the entire book with the unexamined assumption that happy anticipations and happy memories can be discarded as mere illusions - the fabrications of irrational minds. I think he's wrong.
At the end, Gilbert provides a prescription for making decisions: ask the advice of someone who has chosen each of your alternatives, and see how (s)he likes the results. The suggestion is obviously far too facile, but it does give Gilbert the opportunity to discuss the interesting fact that each of us tends to exaggerate his or her own uniqueness. He's almost certainly right about that, but it isn't enough to rescue his advice. Regardless of what the "average" person thinks, I am certain that watching "American Idol" would be an excruciatingly boring experience for me, and that I would much prefer living in Eugene, Oregon, to living in Las Vegas where I live now (and where tens of thousands of people are flooding in every year, all of them optimistic that they will be happier here than wherever they live now). I don't need to talk to another person to be confident that I would prefer a Whopper to anything served in a Thai restaurant, and that I would rather take a course in classical guitar than art history.
So read this with a skeptical mind. But read it. There's lots of good stuff in it.