I have the K2. Love it.
I just bought three books yesterday, and downloaded a few free ones. I've already read through part of them. The Kindle makes it so easy for me to pick up ANY book (I have in the digital library) and read anywhere I want. It fits my reading habit (I don't like carrying a book, let alone two or three, everywhere I go).
I buy REAL books now only if I want to keep the physical copy (like as a souvenir, etc.) or if it's a picture book. Otherwise, if I just want to read text, eBook is the way to go for me now. Convenient, easy to read (with adjustable fonts, search function, bookmarks, built-in dictionary, text-to-speech [so I got audio books, too, for the price of one]) and generally much cheaper prices (on average about $6 - $9 a book).
Also, I download my WIPs to my Kindle and it's made a great difference, to be able to "read" my mss. like a book. Also, the text-to-speech function is invaluable in finding errors.
Also, it makes "beta reading" for other people much easier. No more large computer files or reams of paper. The Kindle can convert most any RTF or text files to its eBook format.
Also, it plays MP3 files so I can load up audio books, podcasts, or music. I can listen to music while I read. That's really great.
A friend of mine has the DX and I'm envious. Yes, it's a little large but the trade PB screen size makes reading so much more enjoyable and it can also display PDF files in their native format (without converting to Kindle format). That's a great asset if you have a lot of PDF documents, including picture books.
p.s. I have just now turned into a Kindle advertisement