OK, the water down the carb thing is an old school trick, and it's not an instant results decarboning fix-all. And if someone is stupid enough, with no common sense, and just chug-a-lugs a gallon of water down the carb, then I guess they got a hydrolocked engine coming to them. Smaller sips and keeping the engine running won't do any harm. When you take a drink of water, you're not going to use a fire hose are you? Treat the engine the same way. And yes, I highly recommend not throwing your engine in the lake to clean it out. That can be bad!
On a semi-related note, here's some interesting reading on water injection:
http://www.motherearthnews.com/Green...on-System.aspx
http://en.wikipedia.org/wiki/Water_i..._%28engines%29

 

there is an experimental 6 cycle engine that uses water injection. after the first three strokes, the exhaust becomes another compression stroke and reheats the exhaust, then injects water into it to create steam. i think its only for engines that are constantly run for months at a time to keep from watering down the oil

as for seafoam, it seems every vehicle ive used it in has caused more issues that what it fixed. the worst was causing the throttle to stick after cleaning it, and the guy wrecked his firebird into a curb

and if water is good to clean, then the engine in my mom's van should have a very clean left bank now that the head fully cracked on it. damn ford