Despite LibraryThing's criticisms, Shelfari has impressed us with its innovative UI. As Alex Iskold wrote in May, Shelfari developed a contextual UI for interacting with individual books. "The remarkable thing about this UI", wrote Alex, "is that it violates a lot of classic principles yet it succeeds in delivering the necessary functions in a contextual and compact way." He goes on to describe this:

"When the user mouses over a book, a contextual popup comes up containing information about the book and a set of associated actions. Part of the popup is a button/menu (sort of like a button and combo box) widget that allows the user to provide information about what he or she did with the book. The first thing to note is that combination of a button in a menu is not standard, yet it makes sense because it saves a click for the most important action. Secondly, the menu is effectively a popup within a popup, which is a big no-no in the classic world, but works well in this context. The elements of the menu are not buttons but check boxes, which allow multiple selection - another violation of classic user interface elements, but which works very well in this context. What is remarkable is how intuitive this gadget is - you are interacting with it in the context of a book and each choice is simple and clear.

Such clarity and simplicity was never present in the old interfaces. Clearly, this new approach to UIs is great, and early adopters are loving it. But will it cross over to the mainstream?"

To answer Alex's question, in a way it already has crossed over to the mainstream - as Borders implemented a very similar design near the end of May. But in general whether Shelfari goes mainstream will depend on how Amazon integrates it with its core business and with products such as the e-Reader Kindle.

Also it's worth noting that Amazon has been busy lately with book-related acquisitions. Earlier this month Amazon announced its acquisition of AbeBooks, an online marketplace for used and rare books. Interestingly AbeBooks owns 40% of LibraryThing!

LibraryThing is clearly worried about today's acquisition. In the above-linked piece, founder and lead developer of LibraryThing Tim Spalding notes that "Amazon can make Shelfari the choice of casual book-lovers who see a button on Amazon.com and click on it." LibraryThing hopes to compete with this by being a superior service. However it's very difficult to compete against Amazon's bulk.

Good luck to LibraryThing, we all love a feisty competitor. For now, tell us in the comments what you think Amazon will do with Shelfari now that it owns it outright.