The display is fantastic! It's super high resolution, quite high contrast, and the brighter the ambient light is, the easier it is to read. The first day after I got it, I sat on a beach in full afternoon sun and it was brilliant. Any other LCD display would have been struggling.
I got the model with both WiFi and 3G, and both seem to work well enough. There was no trouble connecting to my home network, and the 3G works fine even if I'm on the bus. The price of 3G networking is included in the cost of the device itself and books you buy, so there's no contract and I need to have no relationship with whoever provides the 3G. The Kindle now has an experimental web browser which can browse any web site on WiFi but is limited to the Kindle store and Wikipedia on 3G. However, with Wikipedia on free 3G this device actually is the Hitchhiker's Guide to the Galaxy. All it needs is DON'T PANIC in large friendly letters on the front.
For the first few days, I didn't spend anything on content because Project Gutenberg (among others) provide free ready-to-download ".mobi" format files for the Kindle. Downloading books is a simple click and the book magically shows up on the Kindle home page. The first (and only, so far) book I bought was Erlang Programming which I bought on my way home on the bus the other day. The purchasing experience is seamless so I'm going to have to watch that I don't spend all my money on books.
The Kindle comes with two dictionaries built in, the "Oxford Dictionary of English" and "The New Oxford American Dictionary". Both these are books in their own right that can be read and browsed, but also when reading any other content you can point to a word and look it up in the dictionary (you can choose which one is your default). I often look up words to be sure I know what they mean (I'm a big user of wiktionary.org) so having the dictionary available everywhere is excellent.
There are some highlighting and note-taking features, and these seem to integrate into the social media space somehow so you can see what other people have highlighted and annotated. I haven't played with any of those features yet.
The web browser itself feels quite clunky and difficult to use (this is partly because the screen isn't a touch screen and you have to use the little navigation buttons to move a pointer around to point to things). I could log in and use some sites like Twitter, but the browser wouldn't let me type my name into the Gmail login screen for example (I tried both the regular and "mobile" sites). I look forward to upgrades on the browser, hopefully they will correct these problems. But the Kindle will never match an iPhone/iPod/iPad for general browsing capability.
I'm very happy with the Kindle and I believe I will find myself reading more because of it.