Ok, fine. "Blue Friday" maybe has a little better ring to it, but check out the link below to play with a beautiful illustration of what can be done with HTML5 and some numerical differentiation of the velocity field using the Jacobi Method to solve the Poission term.
Sorry, I think I blacked out. What?
Just go here. And play around with dragging your mouse around. Then try hitting the P key on your keyboard. Smoke!