The killer feature is that it reads PDFs natively now (i.e., without having to convert them). For someone who prefers to read on screen and who has to read a lot of PDFs, this is very exciting.
Also, I purchased some technical books via Amazon where the images appear to be fixed resolution. For example, when I resize the text, the illustration still stays small. Sometimes the text in these illustrations are barely readable.
If I purchase the new Kindle, I hope that they will reconvert some of these books so it can take better advantage of the screen real estate.
To summarize: The price of e-mailing your Kindle is now 15c/MB, rounded up.