Well we use a throttle body cleaner and an engine flush made by proform at work.
Our throttle body cleaner is just a carby cleaner, but its not an aerosol, we have a special tool that goes into the bottle and has a valve on it with a tube that can be connected to a vacuum line going to the plenum chamber. You then control how much enters the inlet manifold to prevent stalling. I have noticed the difference this product makes and I for one can definitley say it does good for performance on an older car.
We also have an engine flush, add to the oil and run the engine for 15 minutes. You dont really see the oil coming out darker or anything, what you do notice is the black gunk around the filler cap goes away, when you dip the dipstick after the oil change the oil looks exactly like it went in, no black shit on the dipstick. Again you do notice the difference after its performed.
We also do a power steer flush, add a flushing liquid like the engine flush, change the oil a few times then add the conditioner, again it does make a difference, you can feel the steering being a bit more smoother.
The same thing is also used as a transmission flush, I cant say if it makes a difference or not as I haven't done one of these yet.
I say if your engine really needs it do it, but otherwise dont make it a regular thing at service time.
Phat Drift Damaged
Cobalt Blue 1994 EF XR8 5 spd
Fully optioned - Sunroof, cruise, body kit
Stock as a Rock for the moment