As you might have noticed, I like altering from straight shots and americanos to shots with some other stuff in the cup, like honey, chilli or cocoa. Not everyone likes honey, but as for fresh root ginger, I think it goes with espresso quite well.
Adding a tiny piece alters the taste adding a new interesting dimension in which a full spectrum of the coffee taste can display itself. Adding a little bit larger piece to an americano (depending on amount of the hot water used) just adds interesting spicy tones to it.
This photo shows two slices of fresh ginger; the tiny is a typical size for espresso and the larger could be for 2oz hot water americano:

However, very recently I put a larger piece of ginger to a double shot and I got very interesting taste experience, so I encourage you to try it for yourself.
Much of the taste credits goes to the moment of dropping the ginger to the coffee: for an americano I just pop it right after it is prepared, but for espresso just a while after the shot started brewing.
More photos on this are here: http://twitpic.com/e/14tr (notice: they appear in reversed order




