not all gas is equal. what a lot of companies do is take shitty gas, and just add things like xylene to it to increase the octane. xylene has an octane rating of 114. you add enough of it, and you can get any crap gas mixture to 92 octane. the catch is, xylene puts off a lot of soot when it is burned due to its higher specific gravity. (more carbon) The the idea is, those cleaners will help break up that soot build up. Do they work... yes and no...
The only injector cleaner I've ever seen do anything is that lucas fuel injector cleaner, but with much more in the tank than recommended. I think they say use something like 3-4 ounces for every ten gallons or something... It isn't enough to make a difference, unless you do it over a dozen tanks of gas. I bought the bigger bottle and put half of it in... maybe 16 or so ounces... it made a difference...
as far as the stuff that is supposed to clean the valves, the only thing I've ever had work is Seafoam. pull of a vacuum line, and get as much in there as possible. let it sit for a bit, then start it up, let it smoke like a mother fucker, then drive it once it is done smoking. The seafoam itself will smoke... well, steam off, but if you're motor is really dirty, you'll notice the smoke is more black and dirty looking, thats the carbon buring off... My buddies old saturn actually spit chunks out it was so nasty... then it ran better than it ever did...
I also suggest putting a bottle of mystery oil in the oil too. I don't suggest driving on it all the time, or very hard, but if I'm planning an oil change, that morning, I'll put the mystery oil in and drive on it all day (conservatively) then change the oil that night... Seems to clean decently well...

sorry for the novel, I just have a lot of experience with the chemical additives and crap... hope it helps...