Derek, what problems are you trying to address?
Seafoam is mainly naphtha as a solvent in light carrier oil. Used in your oil it helps clean the crankcase and oil rings. Similar to Rislone, Marvel, and several other simple solvent products. Used in gasoline, it cleans injectors/carbs & upper cylinders. This can mean smoothing out idle, restoring lost power, basically undoing layers of carbon deposits. On the other hand if an engine is recent or has been well maintained you may not notice any effect whatsoever.
Also, solvent-based products for the crankcase should be used very judiciously. They thin your oil & wash surfaces which reduces its ability to protect in extreme conditions. Stick with the instructions and recommended dosage. I wouln't go beyond a driveway idle with a can in the crankcase.
BTW, try searching for seafoam over the last few weeks. I've seen half a dozen threads go by.
Dave
