I haven't ran SeaFoam in mine, but I did put some Champion Fuel System Cleaner (got it at work on clearance for $.25) in my car, and boosted my mileage from 23mpg to 25mpg. Isn't a huge increase, but when one drives 40 minutes each direction to work and back, every little bit helps.
Working in an auto parts store, I do sell a lot of SeaFoam. I have never had anyone complain about it, and we sell a lot of the stuff. I can't speak for everyone, but it seems like a decent enough product.
I know that over on the Ford Truck Enthusiasts forum, they can't seem to sing enough praises for the stuff. (Just chiming in here, not trying to say SeaFoam is the greatest thing since gasoline for your car, but just recording what I've observed.)