Nothing I've ever put it into ever showed any benefits. It led me to believe that people who do see improvements just don't know how to maintain their vehicles properly. I'm not disparaging them, they may just not know how to keep things maintained.. I'm just saying that I've put it through cars, trucks, lawn mowers, motorcycles, and have not once noticed any improvement. I've done the whole "suck it into the intake and smoke out the entire city block" to 'clean my valves' or whatever. No improvement.
I think Seafoam has been proven to stabilize gasoline, like Stabil does. So in theory it could help keep water and ethanol suspended in fuel so it doesn't corrode your carbs.
I always have a can of seafoam sitting around, but I don't believe the hype. Keeping your vehicles maintained properly (keep the gas tank clean, know how to rebuild and clean your carburetor) always works for me. There aren't any miracles in a can. Only people who let OEM stuff degrade to a poor running state, haha.
I have been reading up on Startron additive due to the ethanol thread. It looks like it's a more modern version of Seafoam and Stabil in terms of dealing with ethanol in gasoline. I will probably buy some to have around. All the while not really expecting it to help me out in any way
If you run seafoam through your fuel tank, just don't overdo it. It's pretty potent stuff. You could probably put 1/4 can into the tank and it'd run through fine, but even that is too much.