The 10% thing is worded horribly. Humans can only use 10% at any given time. If you use more then 10% of your brain for more then a short while you risk a seizure. But in fact the amount of the actual overall brain we use is quite large. But we are limited to what we can use simotaniously. The smarter you are, the less of your brain you actualy use at any given time, but you tend to use your higher brain functions more effectively. Generaly people with higher IQ's use less of their brains to preform the same tasks.