I would not expect bounce but looking at the motor description it says it runs upto 1000 rpm with 480 pulses per revolution.
I've removed the motor gearbox, though, so I'm down to 48 counts per revolution of the motor output shaft. And I'm only listening to one encoder channel, so 24 counts per revolution. If I rotate the motor at 230 Hz, then I'm triggering the interrupt every 181 microseconds. I dug up this thread, where someone states that the Arduino can distinguish between 64 and 68us:http://arduino.cc/forum/index.php/topic,19671.0.html
Nevertheless, I hear your concerns. I'm definitely up there in frequency, which might produce an unreliable encoder signal.