I would never do something like that but it works great for things like cracked plastic and such. As a matter of fact, I used it just yesterday evening to fix my shop vac where the plastic housing that holds one of the wheels cracked making it too easy for the wheel to come out of the housing.
Along similar lines to your anecdote, several year ago a guy I worked with said he thought he had a warped head on his engine. Another coworker told him to go to Autozone and get a can of "Dewarpo" , add it to the gas, and it would be like new. The guy, who obviously was not mechanically inclined, actually went to Autozone and actually asked where the "Dewarpo" was. Man was he pissed off the next morning when he came to work.