Gladwell clearly has a gift for writing interesting stories. Maybe he is also capable of being a great scientist, but I don't think he needs to be. The practical usefulness is twofold:

1. His works serve as food for thought. There are far too many topics for one man to research them all. Providing inspiration for further research is a worthwhile endeavor as well.

2. He provides thought frameworks. He reminds me of an old wise man. His writing contains key ideas, while not based on scientific fact, which are useful as rules of thumb. Sometimes decisiveness and confidence is more important than correctness or optimality. Tribal knowledge has its place.