Organizing a Library

For more than 30 years I have bought books, entered them onto a master list of books in my library, filled out 3×5 cards (which I quit doing a few years back), read them and shelved them. But all of this has become electronic. Some are storing things in cyberspace.

Just today a friend of mine asked me about Library Thing. I had never heard of it that I could recall. Should I know about it?

What do folks think of Library Thing and what are good resources out there for organizing a library?