Thomas Fuchs gives us a tip about viewing which elements of a website are powered by the device's hardware. I've never ever heard of this before, but I'd bet it's useful. The hardware accelerated areas show up in semi-transparent red. To use the feature, simply open up a Terminal prompt and write:
$ CA_COLOR_OPAQUE=1 /Applications/Safari.app/Contents/MacOS/Safari
Also possible to achieve in the iPhone Simulator.