Gladwell's books are not scholarly research. They're more like hipster coffee shop conversations, and should be taken with a healthy dose of rigorous skepticism, even though they are usually quite enjoyable.
I think Gladwell would largely agree with this description of his writings, or at least with the part that says that his writings should be approached skeptically and that they don't purport to be scholarly. From the article "Malcolm Gladwell's Method" in the Wall Street Journal on November 15, 2008,
http://online.wsj.com/article/SB122671211614230261.html?mod=...
an interview by Jeffrey A. Trachtenberg:
"[Q:] Do you worry that you extrapolate too much from too little?
"[A:] No. It's better to err on the side of over-extrapolation. These books are playful in the sense that they regard ideas as things to experiment with. I'm happy if somebody reads my books and reaches a conclusion that is different from mine, as long as the ideas in the book cause them to think. You have to be willing to put pressure on theories, to push the envelope. That's the fun part, the exciting part. If you are writing an intellectual adventure story, why play it safe? I'm not out to convert people. I want to inspire and provoke them."
In other words, he's basically an entertainer. Debunking Gladwell is like "debunking" the historical accuracy of Monty Python and the Holy Grail.
The downside is his books ending up in the hands of people whose capacity for entertaining novel ideas far exceeds their capacity for rational critical thinking.
[0] "Bullshit" in the sense of H. Frankfurt's technical term for assertions intended neither to inform nor deceive.