I bought one when they came out and use it constantly. I have over 800 books on it waiting to be read. The problem is I keep adding books faster than I read them, and on average I read 2 or 3 a week.
I get a daily email from an outfit called Pixels of Ink. They offer deals on downloads and highlight 4 free books from Amazon each day. The freebies include everything from cook books to classics to newer web based authors. Thanks to them I'm slowly running out of memory. On the Paperwhite that is.