Before I even signed on to LibraryThing, I was impressed with it's concept. All of the ther services and utulities that we've used/reviewed for the tasks are useful, sometimes extremely so. But they were only useful in the sense that they are for the general public. LibraryThing, on the other hand, is created specifically by readers and librarians for readers and librarians. Pretty cool.
This vibe was re-enforced once I joined the site and started looking around. I've never even heard of the author Alain De Botton, but he has a group solely for him. Other book and author subjects ranged from Scuba Diving to Midieval Europe.
It'll take some to do an in-depth perusal of this site, but I would be willing to wager that there are very few subjects or authors that are not covered.