It is the best PDF viewing solution out there. If you read CS papers in PDF format, it's great.
Wifi and some way to keep in sync with a folder on my desktop (or in dropbox) would sell me completely. I don't want to pay Amazon every time I upload a PDF to the device via email.
How is it better than iPad? I've long wanted large PDF viewer but only option DX was $$$ and b/w. I got iPad for unrelated reasons but fallen into using it for PDF reading. It's great. most my PDFs are image/graph/color intensive .5/11" non reflowable. I need to jump around lots rather than read cover to cover so page flip latency is kind of a killer.
The kindle is much better in direct sunlight or high ambient light environment, and because it lacks other apps, is better for distraction free reading of large amounts of text.
I've used iPad, Kindle DX, and a computer simultaneously -- someone's paper on the Kindle, coding on the computer, and the iPad for all communications activity (the computer was not on the Internet).
For reading journals/journal submissions on the beach, the DX is the hands-down winner.
Unfortunately true, despite having a heavily crippled PDF reader. The zoom is completely broken (100%-150%-200% only?), and there's no scroll function whatsoever -- I don't think this is an oversight; it seems to have been deliberately crippled so people consume Kindle books and not their own PDFs.