I have a Sony eReader, and a 1st Generation Kindle. Doubtfull i'll be buying this new Kindle.
The Sony is rubbish. The buttons are in the wrong place, you have to deal with it's leather case and the books available are few and far between.
The Kindle however.. is a breath of fresh air. I love how it hangs off the Verizon network and downloads very quickly. It even feels good holding it - next page, back etc.. all in the right places.
This won't replace the modern book. Here's the scenario:
Techies - if you're reading technical books 9/10 you'll be scribbeling on them, highlighting passages, drawing circles etc.. as references to future projects or deployments. You'll then potentially go "Hey dBag - read this" to a colleague. They take a beating - Kindles do not work well with this.
Vacation - i took my Kindle to a beach in the Indian ocean (Zanzibar) over xmas, and Kindles do not like the sand. It still works, but i was very cautious with it. It was GREAT not to have to hold pages back becase the wind was blowing it.
Big fan of Kindle, but by no means a replacement for good old time-tested paper and ink. - RC