I must admit I loved my old Sony PRS 505 ebook reader. I like the the e-Ink display and being able to carry around a multitude of books without carrying around the actual books. That said Kindle now has some key features that are of interest to me, and actually the most interesting one is perhaps the simplest thing - being able to pick up a book where i left off from any device.
Sometimes I don't want to carry even an e-book reader with me and so my phone is good for those times I have 10 or 15 minutes to read something. The synchronising page over whispersync then is a key feature for me and has prompted me to sell my sony and get one of the new generation kindles, linked below with a gratuitous advert.
Kindle Wireless Reading Device, Free 3G + Wi-Fi, 6" Display, Graphite, 3G Works Globally - Latest Generation (Amazon.com)