Well I've voted "both are fine". I used to be an avid reader, but with the neurological problems/neurosurgery I've had over the last 5 years it's damaged my sight, and for a long time I gave up reading altogether because without super-large text I struggled to make words out. For a while I tried audio books, but they're just too awkward (either carting multiple cassette tapes around or CDs and a CD player). Fortunately, gradually as the docs get me sorted out little by little my vision's improved a lot, and I have started reading again - my main problem's finding the time to read these days. Recently I've been reading a lot online (mainly BBM fanfic) and that's great because apart from not having to move from my computer
I can re-size the text as large as I want.
Neither the Sony one or the Amazon Kindle have made it over to the UK yet as far as I'm aware, but if recent experiences with the iPhone etc. are anything to go by, they'll be slapping a hefty premium on them when they do make it over here. I've just had a quick google, and there's one called an Iliad Ereader available in the UK for £443!!!
I can buy a laptop cheaper than that!
My problem with all these electronic gizmos is that I just don't trust them not to lose stuff, having had PDAs that have died on me in the past. With a "proper" book short of the house burning down or dropping it in the bath while reading, I know not much is going to go wrong with them, and okay, so I have to dust them occasionally, but they're low maintenance and I don't have to worry about losing them because they're sitting there safely on the bookshelf. A lot of the books I've got, I'll read time and time again, and if I've got it sitting on a shelf, why go out and buy it all over again to stick on a machine? Plus of course there's then the issue of sharing your favourite books with your friends - I'm usually quite happy to lend books to friends as long as they don't write on the pages, keep them for years, or knock 'em about, but Sony's offering according to the Engadget article I've read has the ubiquitous DRM, and reads only PDFs and it's own proprietary format.
All in all, I can see a hell of a lot of reasons why I'm probably going to stick with the physical written on paper ones.