The e-ink screen is very easy to read off of, and does not give you eyestrain, although there is an annoying half second of black every time you turn the page. The text size is customisable by pressing the Aa button, which is handy for .pdf document. The interface is very useable, although a marker to show when you have completed a book would be nice, and if you have a large collection of books it takes a while to browse through them. I have over 1,000 books stored and still have 2GB of space left, so no excuse for running out of reading material and no reason to buy the 3G version if you use Wi-Fi. The Kindle is a little slow when synching, downloading or browsing but it's not a problem once you get used to it. A more major issue is that there is no display of the synopsis of the book on the main page, which, if you are looking for something to read, can be annoying.
The Kindle is available from Amazon UK in either the Wi-Fi + 3G version or the Wi-Fi only version.