I saw little improvement after Seafoam and B12, or even cold water. What did clean the tops of my pistons was about a gallon of HOT water sucked through the PCV nipple on the throttle body using a special hose with a restrictor in to to prevent hydrolocking. I made the mistake of letting it just idle, because my car has an insane amount of vacuum and air flow through the PCV line. That caused water to flow very rapidly, even through the small hole in the hose. It pooled in a low spot in the intake, and when I revved it a bit that water got sucked in on the low side of the engine (not parked level) and I believe nearly filled a cylinder since I heard a knock sound. Keep it above idle, that will lower the amount of vacuum and will help prevent the water from pooling. Make sure the car is parked on level ground when doing this, too.
Misting will probably work, too, but water mist sheds its heat very rapidly, so it might not be as effective unless you use more. As far as how it works, I do believe it's just a steam cleaning, but some have speculated that the water droplets explode when they turn into steam and that is what loosens the carbon.
After you do this, you need to take the car out and spank the snot out of it to loosen and burn that carbon. Get the oil up to full operating temperature for at least 10 minutes to make sure any water that made it into the oil gets evaporated.