A week ago I posted the NXT Dog Sled Team project, which (appeared to...) have a traction problem due to a severe weight balance issue. Now having some fun with the other extreme, this NXT Spinner Bot project has six wheels, but nearly all of the weight is balanced over the two drive wheels in the center, with the four castor wheels barely touching the ground for balance. This gives it a very quick turning ability for break-dancing-like spin turns.
The program provided with this project demonstrates a way to detect collisions by using the rotation sensors in the drive motors to detect when the motors have stalled, which allows the robot to bounce around your room without using any other sensors.