I bought the DX for the large screen so I can read programming books and pdfs on e ink. I like some of the artwork, esp the one of the fish. I think the kindle 4 smaller devices have more contemporary screen savers.
(Also, I'd be fired if I sent internal pdf documents off for conversion... :-)
The DX (and I think also the other Kindles by now) reads pdfs natively, no need for a conversion service.
The only real downside is you can't "flip" through the pages. Reading a book sequentially works fine, any other way is a pain.
I got the DX at the $250 special Amazon had for it last Monday. The price is back to $379.