Topher Kessler, writing at CNet, posted an article with some ways to keep the letters from fading. He suggests possibly using a silicone keyboard cover, but I don't think that would be comfortable. But he also recommends using standard cellophane tape, cut into squares that cover the keys.
You probably wouldn't want to do this to all the keys on your keyboard: the most commonly-used ones are those most in need of protection: E, T, A, I, N, and others. (If you're not an English speaker - or typer - see this Wikipedia article which discusses the most common letters in a number of other languages.)
I wonder if there's not another solution though. While I've not tried it, I would think that clear nail polish might do the trick, and might be better than cellophane tape. The tape is likely to peel up from the corners after a while, but nail polish should stay shiny for a long time. I may try this and see how it works on my already-faded keyboard. Any other suggestions for protecting keys?

