Pretty nifty for just two days of work. If it's something you'd like to pursue then the obvious choice is to incorporate your own Amazon Associate codes into the links and thus earn income from the book sellers (be up front about doing this.) Also you can offer a cheap paid account where you allow the users to do this themselves.

For the widget, it looked somewhat easy to theme, but you may incorporate theming options into the interface as well. Color the links. Center items, etc.

It's a really nice project. Overall I found it quite easy to use, but I think you could improve the distinction between creating new BookBoxs and updating BookBoxs.

Perhaps only showing one of the password options based on where you came from or what your last action was would be a good start.

As everyone else said, there is loads of scope for expansion which is great.

Nice.

Which reminds me, where's that StackOverflow clone that was supposed to be written over the July 4th weekend? Considering all the hullabaloo I'm curious how the final product turned out.

I actually like it quite a lot! To be honest I like the simplicity, and the fact it works and does what you'd expect it to.

Plus you have the ability to do so much with it, like extending it to incorporate your own amazon ref, making it do stuff when you click a book (like display a larger image and the book blurb), or even integrating it with other book services.