Recently I had the opportunity to get Nokia 770 Internet Tablet (basically for free - a loan on indefinite time). I declined. Previously I have owned both a PalmOS device (Visor), and an iPaq onto which I installed Linux. In both cases I couldn't think of anything useful I could use the device for. Otherwise it was just a waste of time.
This time I did have an idea - as a dictionary where I can note down new words, and as note-taker to replace my paper notebook. So I tried to play with it and it has the same problem as other PDAs - text entry. The on-screen keyboard you tap on is next to useless for real-time text entry. The handwriting recognition isn't much better. If you want high accuracy, you need to carefully and slowly draw letter by letter. I wonder why Nokia didn't buy patent for the Palm's Graffiti entry system. (Yes, there is an option of external Bluetooth keyboard. But that is too cumbersome - suddenly you have to fumble around with two small pieces of fragile equipment that you don't want to drop.)
An ideal PDA should come with software capable of learning natural handwriting. Here's how I imagine it could work. First you type in (using a keyboard) a relatively large text. Then you write the text (using your natural handwriting) on the PDA and let it figure out for what groups of letters composite pen strokes stand for.
This learning process would initially take more time, but it would be worth it in the long run. I don't think that today you can find a PDA which can in real-time recognize natural handwriting. Until such time comes, I think I will stick with pen and paper for taking notes