I like the "before you go" popup. *shrugs. I always mark each read with stars. At the same time those stars go on goodreads as I have it linked and I think it tweets it out for me. Its also most always at the end of the book where it should be. Occasionally I close it and keep paging if there is some from the author note. Not a big deal. I always make sure I am at 100% anyway with each book I read.
Not sure how useful it would be to put other books I already own on that page. That is mainly because I own so many how in the heck would it pick.

I make my own reading order.
Obviously most of those features are mostly for those that use kindles with kindle books and like the integration with the system. Which I like. Its another way for me to track what I read. I also like the new features they gave us while back on the home view page, go figure.