There's a common myth that the human brain only uses 20% (or 10% or some other number, depending on who's repeating it) of its capacity.
That's actually not true at all; we use our entire brains, and perform some pretty amazing things with them. A normal human being is capable of an incredible range of tasks--parsing, understanding, and producing language, reading and responding to subtle and extremely complex social cues, integrating real-time information about our environment into a constantly evolving physical, emotional, and social map; solving highly abstract problems; generating abstractions from concrete information; correlating information from a wide variety of different sources...the only thing that prevents people from walking around in a constant state of awe at what we do every single day is the fact that almost all of us do it all the time.
Savants have very high degrees of skill in a tiny area of expertise, but it comes at the price of a single-minded focus that renders them largely incapable of the flexibility that most of the rest of us are capable of. The result may look impressive, and in its own way I suppose it is...but I'm honestly far more impressed by the flexibility, adaptability, and abstract reasoning process of an ordinary human being.
In the 1960s, computer scientists were convinced that true "strong" artificial intelligence was right around the corner. One after another, cognitive tasks that we had always assumed required intelligence were falling; we learned how to make computers play chess, write in calligraphy, diagnose diseases, predict the interactions of drugs, model complex self-organizing systems...all with a proficiency much greater than humans. (They don't even do man-machine chess tournaments any more; even a PC can defeat any human player, including a human grandmaster.)
But what we've discovered is that mastery of a particular cognitive task is easy; it's flexibility that's hard. We don't all walk around with savant-level capabilities for the very simple reason that so much of our cognitive horsepower is being consumed simply by being able to respond to the environment as flexibly as we do. THAT is the amazing stuff.