Kindles are indeed the "iPod for Books" (and magazines, newspapers and blogs). I've had one for a year and love it to death. There's a new one coming out in a couple weeks.
The Citigroup analyst estimates that Amazon (AMZN) sold 500,000 devices last year. And he figures that the Kindle, which he delights in calling the “iPod of the Book World,” will become a $1.2 billion business by 2010.