|Demographics... the very stuff marketing is built upon.|
The numbers in the above link are quite interesting, but it's good to remember they are just talking about hardware. UK readers seem to like computers, but then again computers are already everywhere. As dedicated e-readers fall in price, we'll see their numbers shoot up. Kindle for $99 by Christmas, I betcha.
It's not clear how many books are being sold by platform, but I think the Kindle is the big winner still. The new iPad 2, being thinner and lighter, may help shift numbers in their direction. But it's still expensive compared to a Kindle, and price is definitely a factor.