One of the features that almost all ebook vendors offer is the free sample. You can download the first chunk of most books (the size varies, but it's usually at least the first chapter) and read it for free, to see if you want to buy the book. If you ask me (or even if you don't!), I think this is the main reason self-published authors have any chance at all. It's also a benefit ebooks have over print books; in a bookstore, you can browse and begin reading, but you have to stay in the bookstore to make your decision.
After you download a free sample to your Kindle and then read it, when you get to the end of the sample, there are links to buy the book or to see it in the Kindle store. Previously, when you bought a book that way, the book downloaded to your Kindle, but when you opened it, you were at the beginning of the book. To get back to where you were, you had to note the location number at the end of the sample, and then use the "Go to" menu to get to that point in the full book. It was very cumbersome, especially if you goofed and deleted the sample before you got back to reading the book, because then you didn't have a marker of where to go.
Now, when I use the buy link at the end of the buy sample, it not only downloads the book, it deletes the sample for me, and sets my "place" in the book at right where the sample ended. When I open the book for the first time, I'm right where I stopped reading in the sample. Exactly the behavior I would have asked for if they has asked me! My only complaint would be, why didn't it do this to begin with?
Just to highlight how fast technology is changing, here's a photo of a panel on ereaders that I was on at the Baltimore Book Festival in 2011. Back then the way samples were handled after you bough the book would have been one of my peeves about the Kindle, but now it works great!
I don't know when they added having a button that says "See this book in the Kindle store" at the end of the free sample (as well as a buy button), but I like that, too, because I don't always remember how much the books costs. I'd be interested in knowing if all Kindles have these new features, or if the programming is unique to the Paperwhite. If anyone knows, please post a comment!