translate3d(0,0,0)
From Remy Sharp, this video demonstrates a very helpful optimisation when coding mobile web-apps. Applying even a nullified 3D css transform on an element (using translate3d(0,0,0)) tells iOS to use hardware-acceleration, which results in a much better user interface.
Many of those JavaScript demos you see, showing iOS with low framerates, are because they are poorly coded - not because iOS is slow. This video shows one instance of poor programming, which - by adding one line of code - has an incredible effect on responsiveness.