I think if the Kindle had been available in the UK at the time, I'd have bought it, but since then I've kinda soured on it. One of the charms of the Kindle for me had been the access to their US catalogue. However, if you use the Kindle in the UK, you either have to register it as American, and then pay a 1.99 surcharge for every book, or register it as UK but have much more limited choices that are basically replicated by other UK ebook retailers like Waterstones, Borders and Sony Bookstore. (This is probably best verified.)
Plus there's the issue of the format. Amazon uses mobipocket format for their books. Used to be a pretty widely used format, but sometime after Kindle launched, Amazon bought the company that licensed mobipocket format to other companies, and made it exclusive to amazon. Now, they can't really cancel all agreements right away, but they changed the rules in such way that you can't even have mobi books on the same reader as the other very popular ebook format: Adobe ePub. So, if you buy books from Amazon, and get tired of your Kindle, if you want access to your library, you'll need to replace it with another Kindle.
You have, basically no choice in the matter. This wouldn't even be a problem for me, to be honest, if it was offset by the access to their US website. But as I said above, that's not really the case any longer.
Adobe, on the other hand, licenses their format to pretty much everyone, so if one day I get tired of my Sony, I have literally dozens of other readers to choose from and they will all handle my library with no issues.
I hope all the above made sense.
Now, for the technical questions. You don't have backlight on eInk readers because eInk screen is opaque: it doesn't transmit light. So a backlight wouldn't work. Sony solved this issue with two sidelights. They are mounted on either side, in the bezel over the screen. It is far from ideal, and there are certain trade-offs in terms of reading quality but that's pretty much the best solution that's been offered so far. Not counting the clip-on lights. (For pictures of what it looks like, google "PRS-700" and "sidelight")
As for what eInk actually is, I will not undertake to explain but instead will point you to the smart people at
http://electronics.howstuffworks.com/gadgets/high-tech-gadgets/e-ink.htmBTW, whatever one you end up choosing, personally, I consider the money I spent on my Sony (meaning, just buying the eReader, not specifically the Sony,) to be the best money I spent in probably the last three years, with a possible exception of the Bose Quiet Comfort. And I'm not sure if for sheer utility, the Sony still wouldn't come out on top.
ETA: Regarding replacing my Sony with any of a dozen other readers. This wasn't always the case. In their time, Sony has done a lot of dumb sh!t when it came to DRM, but just recently they switched their entire bookstore from the proprietary LRX format that could only be read on eReaders made by Sony, to ePub which, as I said above, can be read by lots of other devices. Not only that, but if you bought any books from them in the old format, they allowed you to re-download all of them in ePub. This has raised my opinion of the monkeys who make rights-management decisions in that company quite a bit.
ETA 2: LOOK AT THIS DELICIOUSNESS!
http://gizmodo.com/5380942/exclusive-first-photos-of-barnes--nobles-double-screen-e+readerIf the rumors are true, it's coming out end of October (should be announced in Tuesday,) AND will cost less than the Kindle. I want this soooo bad. I can't wait to see what kind of international coverage this baby will offer.