Going back into my normal, native install of XP Tablet and Onenote I can
clearly see that although I select the pen tool, lines drawn with the mouse
do not have antialiasing (perhaps "smoothing" is a better word for this)
applied, yet lines drawn with the tablet's pen and the pen tool do.

It occurs to me that this problem will also affect those who use a graphics
tablet to write in Onenote, because they will also technically be drawing
with a mouse.

Although it is true that the tablet pen input is sampled faster than a
mouse, I don't think that is the problem being seen here because it is not
experienced in Journal. In fact, when doing the same experiment in I just
described in Journal you can see Journal apply the antialiasing (/smoothing)
after you finish each stroke, be it with a pen or mouse.

Justyn.