Yep, that's what it's called.
"Enter what you're reading or your whole library—it's an easy, library-quality catalog. Because everyone else is doing it too, LibraryThing connects you with people who read the same things."
The site lets you communicate with others on this and other books, see what else others are reading or what they suggest, tag books, and link out to swapping sites to trade your texts. Here's the page for James Surowiecki's The Wisdom of Crowds as one example.
I could see this as a useful research tool, to move from one book outward to find other similar work. Not unlike walking the stacks in a library, with the exception that this library is organized by what the online community is reading and how they categorize their works.
More time wasting guaranteed!