This post used to be on Posterous. I rescued my posts before Posterous shut down and am now sharing them here.
I played with the mouse coordinate handling a bit to try and compensate for the rotation, but it's still not great. For some reason, up-and-down movements seem to track well, but left-right movement causes the drawing point to move up and down relative to the cursor.
My guess is that I am just being bad at "the maths" and that I'll get it figured out later. :)
Play here: http://schmarty.net/hershey_js_demo/