i've heard the thing about water in the carb, seafoam, and running midgrade gasoline all doing the same thing. how much of that is true? just for the record too, when I pulled my head, my engine looked virtually brand new as far as carbon build up, and yes, I've run two cans of seafoam through my truck.

 

I think most of it builds up in the intake, rather than the cylinders, but I don't know. My engine was a peice of crap when I bought it, needing a total rebuild, and it was pretty clean. Not sure about the head, though...
Of course I had a bit of a head gasket leak so that was steam cleaning two of the piston heads. But there you go. Even anti-freeze will clean that stuff out, not sure why water wouldn't. I think probably seafoam has some properties that make it better than water, but they may come more with adding it to your gas and oil. I know you can soak things in seafoam to clean carbon buildup, and it cleans it like brake cleaner or carb cleaner, so it's better than water in that sense, but obviously for running something into the cylinders and maybe the intake, it seems like you're just steam cleaning, so water aught to work fine.