This is really great. I love the concept and simplicity.

Here are some suggestions:

1. Use the Amazon API to autosuggest book titles and author names.

2. Normalize the lists. That is, count up which books are recommended the most and use those statistics to recommend books.

3. List similar lists on each list :) Lists that list the same books might be related. If they list two or more of the same books, they're probably related.

But even if you don't change a thing, it's still a great little project!