Techniquely, we do only use a small percentage of our brain power. Although certain areas of the brain are associated with different operations (i.e. the right side of the brain tends to control the left side of the body and vice-versa) it is not generally thought that the parts of the brain that we don't use are in some way associated with special 'powers' that we have not discovered or could somehow switch on.
The human brain is becoming more and more adapted and developed and our ability to understand each other and our emotions appears to improve over time. It cannot be ruled out that, with time, we could be capable of performing tasks now deemed impossible.