I love my DX for reading PDFs. It saves me a lot of frustration in that I no longer have to carry around a stack of file folders or binders of printouts.
Would I like to have more features? Yes, of course. But I'm not one of those complaining about it not being an e-ink version of Skim. Just being able to read so many different PDFs in one very portable device is great!
I should point out that I'm lucky enough to have been able to keep my K1 when I bought my DX, so I do mostly still read novels and such on my K1. On books I've bought through Amazon, the sync feature has proven to be a real boon. I can start a book on my DX, move to the K1 (which I'm more likely to take with me when I go out and about), and then, at night, even on my old iPhone that I keep by my bed that I use like an iPod Touch, the text is sync'd to right where I left off. Very sweet.