You can apparently email PDF files to your Kindle (not sure how - each Kindle has an email address?), and it will be able to be displayed on the Kindle 2 (I don't believe that was available for the original). I can see that being useful for whitepapers, manuals, etc.
I get the impression that if you tried it for personal reading, you'd be sold -- my wife was a traditional book person and now she rarely reads "real" books...