The zombie game I'm working on is where that test originally was, which is here. It's uses the same shadow system, but with a tweaked shadow sprite (basically just a solid wedge of black with a bit of blur to the edges).
I'm just trying to get it optimised at the moment. It runs fine on my desktop PC, even when it's forced to use Canvas2d in IE, but I tried it on a laptop today at it was unplayable. The optimisations I've done (such as culling out shadows when they're off screen) actually loweres the overall fps (especially in webgl, which could handle the extra sprites), but it also smooths it out, so hopefully less dips into the 20's. Plus with the optimisations it also means I can hopefully increase the level size without any slowdown.
I thought using sprites as shadows was a good idea, and it works fine for enemies and collumns and small things, but you need heaps of shadow casters to make a wall (butted up against each other to fill the gaps) which isn't ideal. I can't think of a method to do the walls and buildings in a simple way though. If I could use vectors / polygons this would probably be easier I expect?