WebKit does all of its painting on the CPU and then uploads the results to the GPU in the form of an OpenGL texture. This process is slow, but once you have that texture, it can be drawn to the screen incredibly fast. This is the key to native scrolling speed.

It's amazing to what great lengths people need to go to squeeze in a little more fps, to golf out a little more memory and to save a few more cycles.

More of the good stuff here: http://cl.ly/Aibw