I have a Kindle 3 with 3G that I bought in the USA in November last year. Since then, I've used it in 11 countries including the UK. It works in all of them using Wifi. I've only tried the 3G in a few countries - I don't remember exactly which but I'm pretty sure the UK was one of them. It worked in all I've tried. The user experience is exactly the same as being in the USA. Prices are always listed in USD, and the selection of books available is (as far as I can tell) the same as in the USA.