In regards to 2), something that I really enjoy when reading books on my Kindle is seeing the "popular highlighted passages". It basically shows you in your text where the most popular highlights are (so usually thousands of people have highlighted that passage for it to show up to you). I would love if they would expand that out further and allow popular comments/annotations as well (opt-in, of course)...although I'm sure there are a whole breadth of filtering and spam issues to deal with.
