A broad definition of "gyroscopically stabilized vehicle" might include the Segway. It certainly illustrates some of the questions that arise from gyro control of ground transportation systems, such as "What happens when the gyro control fails?" In the case of the Segway, the answer would seen to be "You fall off."
Falling off a Segway is apparently a real problem and a large recall was recently issued as a result. And it not the first. For more discussion check here.
Another question raised by the Segway is "Why?" I guess I am one of those people who just doesn't see the point of the Segway. I grant that it is an impressive technological achievement, but so was the hovercraft. That doesn't automatically make the technological useful (try running a hovercraft on a dry day in the country and you will find out how dusty the great outdoors really is). Maybe I will post at greater length on this issue. In the meantime checkout this great page on building a balancing scooter.