Gladwell's conclusions are hardly rocket science - guess what, most successful people are clever but not ridiculously so, plus they had a lot of help and sometimes luck, and took the opportunities that presented themselves to them, they practiced very, very, very hard - the 10,000 hour theory - they had a positive attitude towards hard work and do not give up easily, plus (and this is perhaps the most interesting part) the cultural and family background of the individual plays a much larger part in all of the above than you might think, and success often requires that this is accounted for.
Some of the examples are straightforward. The way that children are picked for sports clubs at a young age means that the oldest in the year have a huge advantage - in many countries the vast majority of adult hockey players are born in January, February or March. These children once selected are given many more hours of practice than their contemporaries and so the difference in skill quickly grows - leading to a self-fulfilling prophecy. The series of coincidences and opportunities that placed Bill Gates in the right place at the right time to become the dominant figure in his industry are also well documented and have been acknowledged by Gates himself, and the way that the Hamburg clubbing scene gave the Beatles eight days a week of live music practice and turned them into, well, musicians, seems to add up. As golfer Arnold Palmer once said, "It's a funny thing - the more I practice, the luckier I get."
Gladwell's other examples are more far-fetched and slightly more controversial - his connection between rice-growing cultures and mathematical skill, for example, or the cultural explanation of why, until recently, there were so many Korean air crashes. There is a certain amount of selection in the examples, however he argues his case well each time and is usually, if not always, convincing. This is very much an argument against genetic causality - many of Gladwell's examples are able to rule this out by showing that people from the same genetic background, if living within a different community or circumstances, have very different outcomes.