You may never worry about how pianists are able to play so many notes so fast, but trust me, this and similar issues fascinate experimental psychologists. The problem is that pianists (and fast typists, and many other kinds of skilled people) move their fingers faster than they possibly could in response to straghtforward mental motion commands. The phenomena is called "pipelining", and it's believed that our brains queue long series of commands, so that even as one finger motion is performed, the muscles are decoding the next motion and starting to perform it.
One result of pipelining is that more typing is often faster than less. For example, you've just typed the word "distant" but you meant to type "distraught". All you have to do is erase the "an" and enter "raugh" to correct that word, but likely you'll erase the whole word and type in the new one, which will roll off your fingers faster than you could think "minus an, plus raugh".
But if there's an intermediate change or action you need to do frequently, you can force yourself to learn your efficient shortcut, so that it becomes faster than your natural pipelined way of thinking. I found a nice application of this in the (rather long) address list on my PDA. When I want to telephone the place where I get haircuts, I look up "Mystique." The natural pipelining way to do that is to type 'm' and then scroll through a few screens of alphabetized m' entries. But with some effort, I've trained myself to look up Mystique by entering 'n', and scrolling back one line.