Just got a kindle 3G. Possibly one of the worst user interfaces I have ever had to use. Absolutely hideous. Reading on it is OK (but only OK), doing anything else is genuine nightmare. 5 years ago it would have seemed good, but after the iPad it is just inferior. Yes it is vastly lighter tahn the iPad which is good but it feels fragile and fundamentally rather cheap and throw-away. If you are travelling and don't want to carry a ton of books it will be useful and it is cheap enough that if it get lost or stolen it is not a huge issue. But a good user interface, no. Of course the fact that e-books are stupidly expensive and can't be shared does not help.
and no PDFs....
Lynn