Usability 
A social network for book lovers. LibraryThing lets you build an online catalog of your books, rate them and write reviews. It gives you recommendations of new books you may like based on the likes of other members with similar tastes. There are links to Amazon and other online booksellers. A basic membership, allowing you to catalog 200 books, is free. Unlimited cataloging is $10/year or $25 "for life". Social networking features include a profile page for each member, groups, forums friends and the ability to privately "watch" a member's updates.
Compared with the desktop version, LibraryThing's mobile site is quite limited. It lets you view your book catalog and look at the site's recommendations. There is no ability to add books to your collection, read reviews or interact with other users. Recommended by: @andrewjb44