Seafoam is good stuff. I grew up in Minnesota, where it was first available, and my dad has used it for years on everything from winterizing his old cars to snowmobiles and tractors.
If you use it in the crankcase on an older car be warned that you may develop oil leaks...not that that leaks are caused by the product, but that it can disolve the sludge that was formerly plugging the leaks.
I've used a few cans in the gas tank on my 2011 GT. A nice side benefit is I think it makes the exhaust sound more burbley when downshifting.
2011 GT Coupe Premium | MT82 | 3.55's | 400A | Red Candy/Stone | Security Pkg | Built 7/21
Installed: SVT Axelbacks w/ res delete, FRPP tune, K&N drop-in, strut tower brace, JLT oil catch can, PIAA/LEDs, GT500 splashguards, 27% tint
Sold: Rebuilt 1994 Mustang | Motorsports 5.8L/351W | HD 5M | DF clutch | 9" rear end 3.73s | Cobra 'R' brakes | aluminum driveshaft | street legal in SC (barely)