I posted a few pictures on my blog that show the same book on all three Kindle devices (so, is the new one Ki, to go with the K and K2?). The screen is very clear on the iPhone, but graphics are extremely small. The blown up photos show that if the screen were bigger, it would be quite readable, but it is so physically small that I had a hard time reading the box on the sample page (which was the first graphic I blundered upon, not one I picked to make it look small).
http://booksontheknob.blogspot.com/2009/03/kindle-iphone-pictures.html Really useful. There's a lamp hitting the K2 in the 2nd picture which makes it less contrasty.
What surprised me is that the background to the iPhone is so very dark gray. Considering all the dark-gray threads about the K2 threads, more should see this. However, the crisply dark black they use for the fonts is an important element and somewhat missing on the K2.
With the K1 and K2 in some light, the K2 basic font tends to be more like fine-point pens (which some find 'crisper' or 'sharper' and others find 'dimmer') while the K1 is like a medium one. Some people prefer one over the other. But I hope the general font shade eventually will be darkened via whatever mechanism they can use, which is said to be possible through via a decision/change to the current software definitions of the font.
Nice blog, Karen!