It's a magical size - exactly small enough to slip into a back pocket like a chunky phone, and exactly large enough that it's actually practical to use desktop software on it. It's ergonomically first-rate - I've done CAD work on it. And it's durable too - I've dropped it several times already and it's barely even scratched.
It's also unlocked a class of activity I didn't know was possible - long-form writing while out walking. I can get 50wpm with great tactile feedback on the tiny keyboard. It's all in on thumb typing, and having struggled with a Cosmo Communicator for a year I can absolutely say that that is the correct decision for a mobile device. The vast majority of the time there's no handy surface nearby.
Now that I essentially have a laptop on me at all times, phones hold no appeal for me anymore. None. This is the class of device I've always wanted. All it really needs in order to replace a phone completely is a cell modem which can wake it from suspend, and ideally the standard "mobile" sensors such as GPS, cameras, and gyros. And waterproofing, I guess.