Very easy to use, because you can add books with ISBN numbers, so it doesn't take too long to add a stack.
It's a work in progress. This also drives home the need for me to grab the rest of my books from my parent's place. Well, I wouldn't call it a need, just a burning desire that controls my existence.
It also has a nice "in common" link, which shows other user's libraries that have the same books as yours, so it's a good way to pick up recommendations.