I've used it on the last two V6 Fieros I've owned, and it's done a relatively good job. The stock PCV setup gets a lot of residual oil in the upper plenum and intake, so this helps to burn it all off and clean most of that up. As Orge heeds in one of those threads, be careful with some four cylinder cars because they have a filter in-line with the brake booster vac line.
You're going to read varying degrees of using it in the actual crankcase. I always wait until it's oil change time, then run a can through the crankcase, drive it for about 20 minutes, then change the oil. Don't put the product into the car and drive around like normal. It can cause oil leaks to appear if you didn't have one before, or make a present leak more pronounced. Or it may do nothing of the sort at all. Your results will vary.
For as cheap as a can costs, it for sure doesn't hurt to run it through the intake at the least.
I take the vacuum line from any source on the intake and stick it down into the can of seafoam keep the RPM's up on the engine until the entire can is run through the intake .it will smoke like hell but will definitely clean out the intake and valvetrain and piston and rings.I love the stuff