I prefere this one:
http://www.youtube.com/watch?v=66RBfrBgL2E

Your Video is on a iPad. On an iPhone with the same size of the n900 you couldn't even draw 1 line.

The user of the iPad needs special wearing and and special stylus.
He can't draw details because the screen is not pressure sensitive.

What he does is very dangerous. If the pinch gesture is not correctly recognized he will have a false line instead of a pinch gesture. I preferre the buttons on my n900 that are less dangerous for such an exercise.

In this case a mode change would be very useful. But the iPad has not enough buttons.

It's better to paint on the little n900 than on the big iPad. Because the screen and the buttons are better for such a work.

But for panning and zooming there is no mode change needed. Panning is done by the swipe gesture. Zooming and Rotationg are done by tap&swipe.

If you want to work without buttons like the user on the iPad I propose a standard tap&hold for mode change: Between drawing and moving.

The n900 is much better for painting than the iPad that is much bigger because the concept of the n900 is more intelligent.