A common metric authors and other interested folks use to ascertain the success of a book is to examine its Amazon.com sales rank. Brad Abrams took this idea and went a little further with it, ascertaining a book's popularity not only by its sales rank but also by the “buzz“ it had generated in the online world. Brad says that he determines the “buzz“ value through the Google API, although I'm not sure what the numbers correspond to. When putting in the book's title, I don't get nearly the same number of results as the “buzz,“ and I can't find the code Brad uses to determine the “buzz“ in his blog entry.
Regardless, Brad's approach is on the right track. My only concern is that the “buzz” rating might be a bit skewed based on the words in the title of the book itself. For example, the book Programming C# is probably more likely to result in false positives on Google (i.e., pages that use those words or that phrase that aren't talking about the book) than, say, Teach Yourself C# in 24 Hours.
You can check out Brad's results here: