Personally, I have seen people use Newtons to take notes in class, but on rare occassions. I think to get it working you would have to open a text doc. within the newton and manually inscribe the letters one at a time, which would really tick me off.
Why not bring your Firewire iBook to class? I think that would be a lot easier overall to take notes using the iBook, where you can type some 40+ wpm, rather than using a Newton, which only gives you maybe half that.
When I plan to go to college in a little over a year from now I plan on bringing a Titanium Powerbook (or my Firewire iBook, if I do not get a G4 replacement) to take notes. I can see what I type, since I have poor handwriting, and I have the convience of bringing a portable supercomputer with me to class.