I currently own a 2nd generation Kindle.
I have to say, my experience with Kindle has been nothing but pleasurable. I've been reading far more than I had before I got the device. Using calibre, I've been loading my subscription to the Economist and actually go through most of the articles that I'm interested in reading.
The bookstore interface is seamless. You purchase a book from Amazon bookstore either through Kindle wireless connection or on your computer, and the book arrives through Whisper.net. I just bought "Big Short" by Michael Lewis and finished more than half-way already.
I had a chance to use iPad for a bit when I visited Chicago and I have to say that the device felt fairly hefty compared to Kindle. Although it's not a heavy device when you consider the device as a replacement for a laptop but as an eReader, I'm not sure it's something that I want to use it for an extended period of time.
BUT, reading PDF has not bee very pleasurable on Kindle. I'd imagine a bigger screen from Kindle DX would make it better reading experience than normal Kindle as far as PDF documents are concerned.