How is fuel injection service performed?

I still agree that it's a waste of money as a preventative maintenance on a good running engine. I don't agree that plugged injectors are a rare thing though. The worst case I've seem was an F150 that ran so poorly the customer towed it to my shop. The owner had already replaced more parts than you would believe. Two cans of BG Injectaflush later the thing ran like a new one. The owner of that truck was just plain stunned.