I have run seafoam through two cars of mine with only good results, my E28 533i and my Audi Coupe GT 2.2. Basically you just start the car (make sure she's nice and warm), find a good vacuum line that can be disconnected without the car stalling, and stick it in the bottle of seafoam. Generally one enough starts making its way to the cylinders you have to manually open the throttle to keep the car running, and then the smoke show starts... Depending on the car you can get a steady little stream of smoke like in my E28 which was well maintained, or a huge plume of smoke like my Audi...
In both cases each car seemed to idle smoother, rev smoother, and get better mileage. After using seafoam in my E28 I was getting around 28mpg out of a 12v 3.2 liter inline 6!! Mind you, they were rated at something like 23...
I have not done it to my Euro spec 6 series and I do not plan on using it on my 164, since they are both rare beasts and both have high compression engines... Something about it just does not seem like a great idea.
FWIW: Sucking seafoam directly into the intake has a very similar effect to water injection used in turbo applications as far as engine cleaning goes. It basically just burns the carbon off of the pistons and combustion chambers. You can use regular (distilled) water to achieve the same effect, though it will take longer.
