Kevin Rose posted his ideas for ebooks, and a few are good, but my favorite was an online book club.
I’m not very interested in seeing or hearing friend’s annotation of specific parts of a book, but rather reading books with friends and then discussing them when we’ve finished. Books—fiction and non-fiction—spark deeper and more meaningful thoughts than online writing tends to, and I would love to discuss each book I read with others.
That would be a fabulous web application if done right.