Much well-deserved drooling over the Kindle DX. The killer app is native PDF support: as Michael Trick pointed out, the earlier Kindles didn't do too well with math support (the native Kindle document format is not PDF). I could easily see myself using the DX at conferences, rather than lugging around my laptop, or (worse) printing out copies of papers I wanted.
The Kindle has a nice feature that you can email documents to a specific address and have them synced automatically to the device, but it comes at a price ($0.10/document). If you use a direct transfer over USB though, it's free of course.
What I don't understand is why this has taken so long to happen: it seems to me that the academic market is the killer market for the Kindle: can you imagine transferring ALL your PDF papers to the Kindle for reading ? not to mention books ?
p.s for those of you who will no doubt point out that other readers exist that can read PDF, and are puzzled by all the hype over the Kindle, I leave you to your Archos MP3 players and Opera browsers.
p.p.s I spotted my first Kindle in the wild a month ago at a conference. It was rather cute looking. the DX will be much larger of course.