I too use pencil and paper when I really need to "think", but I think for most things a stylus is the wrong sort of input for what you want to do with a portable device.
For consumption tasks, browsing the web, etc, a touch interface is far preferable. For those tasks where touch isn't sufficient, a stylus isn't at all better. A stylus just doesn't work without the tactile response of paper (which the textured Wacom tablets can offer but a portable device can't).
That hasn't been my experience (I've been using a tablet PC for the last 3 years). With a precise digitizer and good software, stylus-on-screen writing isn't very different from that of pencil on paper. The convenience of permanence/editability/easy sharing vastly outweighs somewhat inferior tactile feel.
For consumption tasks, browsing the web, etc, a touch interface is far preferable. For those tasks where touch isn't sufficient, a stylus isn't at all better. A stylus just doesn't work without the tactile response of paper (which the textured Wacom tablets can offer but a portable device can't).