On the whole, I think I'd recommend the book. But I do think that Ariely badly misfires in his Chapter 5, "The Influence of Arousal: Why Hot Is Much Hotter Than We Realize." The main thesis of this chapter is that humans grossly underestimate the effects of future sexual arousal on future decision-making. For example, in their 'cool' state, humans tend to predict that they will behave, while aroused, in ways more responsible and moral than they in fact do. This thesis is eminently plausible, and Ariely is right about its implications for, for instance, ideal sex education. My problem with his discussion is that his experiments don't remotely establish his claim, but he pretends that they do.
As I said, his claim looks pretty plausible anyway, so criticizing his experiments and presentation is in some sense intellectual. That, obviously, isn't about to stop me.
Ariely describes himself as "study[ing] decision making under sexual arousal". The experiment went like this. He got a bunch of undergraduate men to volunteer for his study. And he asked them a bunch of questions about what sorts of activities they'd predict they'd enjoy while sexually aroused -- would you enjoy having sex with a 50-year-old woman?, etc., and a bunch of questions about whether they thought it likely that they'd engage in immoral activities for sex -- would you drug someone, or lie to someone, to get her to have sex with you?, etc. Then he asked the same questions to the same subjects while they were masturbating; it turns out, young men rate themselves as more likely to enjoy having sex with a 50-year-old, and more likely to lie to a woman to get her to have sex with them, when they're sexually aroused.
From this, Ariely concludes that unaroused individuals are very bad at predicting what they'll be like when aroused. He writes:
The results showed that when Roy and the other participants were in a cold, rational, superego-driven state, they respected women; they were not particularly attracted to the odd sexual activities we asked them about; they always took the moral high ground; and they expected that they would always use a condom. They thought that they understood themselves, their preferences, and what actions they were capable of. But as it turned out, they completely underestimated their reactions.
No matter how we looked at the numbers, it was clear that the magnitude of underprediction by the participants was substantial. Across the board, they revealed in their unaroused state that they themselves did not know what they were like once aroused. Prevention, protection, conservatism, and morality disappeared completely from the radar screen. They were simply unable to predict the degree to which passion would change them.
This looks to me like a dramatic overstatement of the results. What Ariely showed is that the predictions made while unaroused were different from the predictions made while aroused -- not that the predictions made while unaroused were incorrect. Nobody tested these subjects to see whether they really would enjoy having sex with fifty-year-olds, or whether they really would drug a woman to rape her, or whether they really would skip the condom. For all the experimental results showed, it was the aroused individuals who overestimated their willingness to engage in these behaviors. This does not strike me as an implausible possibility; masturbation comes with a significant degree of fantasy, encouraging people to abstract away from, e.g., the moral complications of extra-solipcistic sex. An optimist can hope that many subjects will treat actual potential sex partners with more respect than they are inclined to report that they will while masturbating. Anyway, Ariely has given us no reason to prefer his interpretation to this one.