Points against that:

- I can have a wacom (or similar) device connected to the desktop

- I can even .. use my android tablet as mouse/touchpad/wacom simluator

The benefit: The result instantly on a bigger screen (and maybe even a really big screen if I connect the desktop/laptop to a projector or something).

I know you can't see upvotes here, so I hope it's not useless to post a 'me too' type post. Just to say I'd definitely pay for this on a desktop, I doubt I can draw more accurately with my finger than a mouse and your algorithm isn't bad at all - I have no doubt it'd translate brilliantly.

Actually I think you might be wrong about that, the shape recognition and the way you draw a simple line between two objects to join them would be useful even with a mouse.

Some of us have touch screens on our PCs too :).