The update I applied seems to make the Kindle a bit more responsive. Some of the books—but not all—seem to have better typography (e.g., they have curly “smart” quotes rather than straight "dumb" ones). So I’d say the update was worth the effort to download and install, but nothing spectacular. Ultimately, when you have an iPhone (or an iPad) then the user experience of a Kindle is going to be pretty “meh” no matter what.