I have heard a lot of people hold down the gas and let their motor hit the rev limiter for a few seconds. I guess they think it sounds cool, but wouldn't it hurt the motor after awhile? I know the ECM cuts out the injector pulse to prevent it from over-revving so would the lack of fuel for a split second every half a second do damage to the pistons?

yes over time it will.... thus why you shouldn't be doing that anyway.. reving it is ok... just don't bounce it off the rev limiter