This has been covered many times but bottom line is that the majority of people who says "it works" aren't seeing a great increase in gas mileage and when they see anything at all it's mostly due to the fact the engine wasn't in tune in the first place.
Hydrogen/Oxygen gas has different burn characteristics than Fuel/Oxygen. In a tuned and properly running engine it'll degrade the combustion process.
"The 300ZX Turbo is a dance; it's a song; it's rolling, roaring automotive art. There is no color that doesn't suit it. There is no mood-lifting chemical substance it can't replace." - Automobile Magazine
