Phil Gyford decided to take an old fashioned pen and paper, a MacBook laptop computer, an Apple Newton MessagePad 2100 with handwriting recognition, a Palm Vx with Graffiti input, a Palm 650 with a physical keyboard, and an Apple iPhone 3G with virtual multitouch keyboard and see how long it took him to enter a well-memorized 221 word passage.
The MacBook keyboard won, of course, with the iPhone second and the Treo and pen and paper a close third and fourth. Newton and Graffiti handwriting recognition didn't fair nearly so well.
It's not scientific and not presented as such, it's just one individual's test to see how well he did with his devices.
For me, my handwriting is near-illegible, I type fairly well on a MacBook (but am not a touch-typist), I never liked Graffiti, and avoided typing on my old Treo 600 and 680 like the plague. The iPhone can't compete with my MacBook for text entry, but then I can't easily carry my MacBook in a pocket the way I can my iPhone. Trade offs.
If you have a collection of different devices around as well, and are willing to invest the time, let us know what your results are like.