When I was young broke and stupid and drove a Honda Trail 90 around as transportation, I liked to dump a whole bottle of octane boost into the tank every once in awhile. Wow, what a difference it made in power! Especially since the tank only held a gallon or two.
It sure made the bike a whole lot more fun though. At stoplights I'd drop the gearbox into neutral, wind up the engine, and on green slam it into gear and hang ten through the intersection. The bike had a centrifugal clutch.
Eventually the cylinder head couldn't take the abuse anymore and it kinda sorta blew up on me one day.
I have on occasion used octane boost in my vehicles and it does seem to make a difference depending on the car. Haven't tried it in the Focus yet but I wonder how it would run if I put 12-gallons of the stuff in the tank? Hmm...