Monky:
i have never used sea foam and never seen the need for it. So i can't comment - I think it's a dual action product, and affects fuel AND oil (and can be used in oil), so that's why the OC afterwards, I think. Many horror stories about hydro locking engines, too...
I don't see the need to use a product like that where i have to feed stuff through brake lines, and go into all that, and risk something, etc.
If you use good gas, drive the car at hwy speed at least once a week and do general good fuel practices, I think a normal fuel additive is all you need once in a while...might not need one at all, really - but it doesn't hurt, so i do it when i think of it - not in any regular interval, but probably roughly every 10-15k miles on our cars, neither of which ever had a fuel/injector related problem.
Regular Fuel additives like the ones I listed have no effect on oil, and they DO NOT go in oil - only in gas tank. So there's no need for oil changes afterwards (unless your engine has a serious problem of oil/gas mixing) - so just put the recommended amount into an almost empty gas, fill up, and you're done.
I have NEVER heard of any of those regular additives thinning out oil or anything like that - they're strictly in the fuel.