This, in many ways, is the "self-help" book for people who don't read self-help books.
Its conclusions probably won't surprise anyone - the way to find happiness is mostly just what Socrates, Jesus, Buddha et al suggested - be nice to people, do a job that satisfies you, stop chasing after material wealth, etc.
All of which might lead you to think there's no point in reading it. But there is. Haidt is that rare beast, a serious academic who can write engagingly for the general (educated) readership. Somehow, seeing his synthesis of many, many areas of psychological research creates a real feeling of enlightenment, and I would be very surprised indeed at anyone who didn't find some serious "food for thought" within its pages.
Did reading it make me happier? Well, this is where I'm supposed to say "Well, no, but...", but - to my own surprise - the answer is actually "yes"! Just a little, but enough to justify making the book a "keeper".
Read it, and think about the way you live. Highly recommended.