Invisible, indeed!

The book The Invisible Web: Uncovering Information Sources Search Engines Can't See, cited in John Battelle's book The Search: How Google and Its Rivals Rewrote the Rules of Business and Transformed Our Culture, describes the problem posed by the unsearchable areas of the Web, such as subscription-only databases. Intrigued, I scooted over to the Invisible Web's companion website, only to find the web is actually just a little bit more invisible than I thought: