I have a Kindle DX and am mostly happy with it. I like the larger screen size and being able to get a book immediately, for example. I can load PDFs onto my Kindle, which is great.
I (really) don't like the fact that the publishers are starting to increase prices for electronic editions of books. They all used to be around the $10 price point, but prices have been going up lately. I'm extremely hesitant to buy an electronic book that costs almost as much as hardcover. This problem is presumably not isolated to the Kindle.
Amazon could improve the UI.
I was thinking about getting an iPad for other stuff, and I played with one in Fry's last weekend. For me at least, navigation was awkward. Also, I don't know how fragile it is when dropped. iPods and iPhones are very fragile, so I'm reticent to trust an iPad.
Just my two cents!
Val