I tried it on a Fujitsu tablet pc and found it quite unproductive. It's a good idea, but even after several days of exclusive use, I was still more preoccupied with the act of sliding than with the actual content of what I was writing.

That is what I actually like so much about natural handwriting recognition: It may be not as fast as keyboard input, but the interface is so natural that you are only thinking about content, not about input.

I used to write entire novels on my Newton, strained only by the less-than-perfect screen quality of the device. Then again, the Newton was designed around pen input; I so wish more people would actually take a good look at that UI and creatively copy it.