A great book and worth the read, but like many Gladwellian books, it can be summed up easily. The basic point is that there is no such thing as a true outlier. Success, it seems, is due primarily to hard work and circumstance - brains play little part.
Gladwell went through several (fascinating) examples proving his thesis - people such as Bill Gates, Joe Flom at Skadden, Oppenheimer, some failed genius named Chris Langan. All of them had two things in common: they spent over 10,000 hours doing what they did, and they had fortunate circumstances that let them get ahead of everyone else. Bill Gates was smart, but so were lots of other geeks. He had the advantage of being 16 when the computing age came about, and being possibly the only 16 year old in the country with access to a computer - and he spent all his time on it. By the time he hit college he had well over 10,000 hours of computer time and was arguably one of the foremost experts in the country.
One of my favorite bits was the music study on page 39 that compared musicians, and "couldn't find any 'naturals'" - the skill of each musician at comparable amounts of practice was equal. It's kind of validating to hear this, as many of us have this feeling that there are naturally smarter people out there than us. But apparently this isn't true - and I think my personal experience agrees with this. The harder you work, the better you can do.
One other big takeaway was how circumstance can change things. The hockey league study and elementary school studies were fascinating and relevant. Basically kids that are in the older third of their class (or hockey league) have a natural advantage when they're really little. They are the kids who make all-star, and get extra coaching, and because of that they practice more and thus do become better by the time they are older. I was held back in pre-school so I was one of the oldest in my class, and I definitely think it helped me. Hmmm now can I plan my kids to be born to be the oldest?