When I first learned about Android and iPhone, it was fascinating to see, but I didn't leave my old Nokia phones before I saw somebody demonstrate to me, that it was actually possible to operate these phones with one hand. My Nexus One is still mostly handled with one hand, meaning that I don't use multitouch pinch-to-zoom much, even though it is available, instead I use the zoom buttons on-screen.
However, I still cannot type on my Nexus One with one hand, without looking at the on-screen keyboard. Also, physical keyboards produce higher typing speeds than on-screen keyboards, so the current solution isn't optimal. Also, the Nexus One only has 3 physical buttons: Volume, Activate and the trackball. Everything else requires you to look at the phone. This choice is not optimal: while handling the phone in an unlocked state, you may easily adjust the ringer volume by accident (!), so there are applications that restore the ringer volume, in case you do this. Also, it takes much more time to activate and unlock a Nexus One, than to unlock a modern Nokia phone. The phone is great, no doubts about it, and Nokia is seriously behind these days, but there is still improvement to be made.
In a recent CNet review of the Kindle and the Nook, the reviewer gave Kindle significant more points on usability, mainly because it had dedicated buttons to support the operations that the user did most, whereas the Nook's touch-screen was not as easy to operate. Considering, that we get more and more devices, it is also fair to assume that the devices get more and more specialized, meaning that it will become increasingly easy to identify frequent operations that should be supported using special buttons, and that the best devices will get more physical buttons. Who knows, maybe we will see bluetooth remote controls for Android phones, that enables you to do calls and write SMS messages without taking the Android phone out of your bag. I would buy one.