Kindle can read pdf (and word, and text, and ebook... among other) files, but the books that Amazon sells are in their own format.
I love the Kindle. It's gotten me back into regular reading because it's so easy to always have with me. I've gone from reading just a few books a year to over a dozen books in just the last few months. I like to read two or three at a time, like some Sowell and then some Heinlein, depending on what I feel like reading at the moment. This way I've got them all with me all the time. Any time I've got a few minutes I can pick it up and keep reading.
I also like the built-in dictionary. If you're not sure of a word you can just highlight it and get the definition.
By the way... anybody that hasn't read Sowell's "Housing Boom and Bust" book-- get it. It's gonna really enrage you. :-)