Testing inconsistent results between browsers for clearing the canvas by resetting the height or width to the value it's already at.

Basically it seems that what it says about resetting the canvas at http://diveintohtml5.org/canvas.html is wrong for WebKit browsers - you have to change the dimensions. A more correct doc is http://webkit.org/blog/176/css-canvas-drawing/
Browser Result
Firefox 3.6.8Works
Opera 10.xWorks
Iron 5.x (Win7) Fails
Safari 5.0.1 (Win7) Fails
You have a crap browser that doesn't support canvas

click this to clear the canvas (by setting width to 800)
click this to clear the canvas (by toggling width between 800 and 801)