That's a great idea, and I really like how it looks (and how usable it actually is for a first release). The only flaw I see is that the most popular questions on SO are those with the most views and upvotes, thus those everyone can understand and appreciate the value of. This is fine, but it also means that they're the ones most people already know the answer to. That means I might not use your tool to learn more on…
I was going to say the same thing. Perhaps a better metric of interestingness would be questions that more than one highly reputable user has answered or commented on. The larger number of reputable users, and interactions between them, the more interesting the question/answer.