Hi!
I've read the news about the Kindle Developer Kit, and I think it's a great chance to help grow the Kindle community and make ebooks more popular.
I remember BookCrossing was fashionable a few years ago in my town (I live in Milan, Italy), now I don't hear much about it anymore, but if you could lend ebooks, or just leave them tied to a location (an airport, a train station, a park, a restaurant...) for people to pick them up, wouldn't it be great for the Kindle community?
An Ebookcrossing app could allow users to create quizzes or games and put an ebook they own at stake, or maybe simply creating virtual shelves in specific places, where you can donate one of your ebooks and take one in exchange.
Maybe ebooks would be readable only in that location, but well, these are just ideas I'm thinking about while I'm writing (I wrote a
blog post about it yesterday), I'd be happy to hear the opinions of Kindle owners and developers as a comment on the blog or replying to this thread