It is not even primarily marketed as an emissions testing aid (like some products). It is supposed to remove carbon buildup, clean injectors, remove moisture from the fuel and oil, free sticky piston rings, and stop world hunger, among numerous other things. You can put it in your gas tank, crankcase, or feed it into your intake. I only fed it into the intake on the Mercedes.

My son heard about it on the Toyota MR2 message board, where at least one member had very good luck with it. His compression results before the treatment were 190 191 187 192, and after the treatment, 184, 185, 183, 185. The link to the thread is here:
http://mr2oc.com/showthread.php?s=&threadid=18533
But I believe registration may be required to view it.

One drawback of seafoam is that your car will emit a noxious billow of smoke during treatment, so you will definitely want to do this in a well ventilated area, preferably away from your neighbors.
To give you an idea, someone posted the following picture on the MR2 board:


Here is some more information:
http://www.seafoamsales.com/motorTuneUpTech.htm

Hope this helps

Michael