The first hundred or so tutorials I studied about the canvas element focused on drawing lines, shapes, paths, strokes, and fills. These functions are appropriate for drawing on the canvas when speed isn't a priority, such as when drawing graphs. I noticed that my earlier test animations ran somewhat choppy, so I was interested in seeing if there is a faster way.
I decided to test if using drawImage to blit a sprite would be faster than actually drawing an image.I prepared a simple graphic (blue rectangle, black border, thick black line in the middle) and put it on the screen with line functions. I took a screenshot and saved it as a gif. I then ran tests drawing the same graphic both ways, 10,000 times and measured how many millisends it took.
This test (at least on Firefox 4) shows that copying images takes about 1/5 of the time of drawing a simple image with moveto and lineto. Just to double-check, I went back and edited the file to put a big transparent hole in the middle. There wasn't any noticable difference in speed, although the end result looks like it's broken. :)