[artdutra04]

Arduinos are great fun to play around with, but they are very limited in what they can do based on their limited number of ports and processor speed. But their low (about $20 USD) price point and free, multi-platform IDE makes them very popular for hobbyists as you pointed out, who may want a cheap microcontroller for projects that don't have to generate PWM signals for a dozen motors, process lots and lots of serial communications from the radio, or handle a dozen different sensors of various kinds.

If anywhere, they may have a lot of potential in the autonomous beetleweight or antweight combat robot competitions, or in the Trinity Firefighting competition, or any other competition which deals with smaller (less mechanically complex) robots with a greater emphasis on control and sensors.

EDIT: As for whether you can use an Arduino to contro a FRC robot, the answer is yes. You can pulse the digital output ports to generate PWM signals (you'll need a 'scope though to test their waveform and troubleshoot), you can buy the RS232 serial boards for serial communications, and you can read sensor inputs. Just note that you will be very limited in all of these areas, unless you daisy-chain several together and implement a master-slave communications protocol to help they all handle different functions of the robot.