If you are running at least Mac OSX Snow Leopard or a recent WebKit Nightly, these animations should be hardware accelerated. If you are using another WebKit-based browser, these animations will probably still work, but they'll be a little slower and jerkier because they are running on the main CPU.
Notice how the text is using @font-face from TypeKit but is still selectable with the mouse and updatable via JavaScript all while being animated by CSS.