I will say this, at over 100K, I had no visible "crap" in the bottom of my fuel tank.
Well, other than sugar, which is why I dropped it in the first place.
omg, who did that? mythbusters did a special on that and the sugar had no effect. i wonder if it would be different between a fuel injected motor though, they tested it on a carbed one and i wonder if it would clog the injectors or just dissolve.