Fuel system additives, Good or bad? Options

[senick]

So I've heard some negative things about fuel additives for cleaning the fuel system, and I'd like some conversation on the subject. I've been using Gumout fuel system cleaner about every oil change thinking that it was an altogether innocuous compound. But I've read comments on here how similar products can damage the emissions components. I've recently had to change my 02 sensor, and I'm thinking that might be related to my use of gumout.
Are there any good products will no negative side effects? Is there even reason in the first place to use these?

[Galcobar]

Fuel additives were a bigger thing back when gasoline was not sold with detergent already added into it. Now, they're a lot less likely to be important. Gum and varnish are largely dealt with by the detergents in gasoline.

Regular additions are unlikely to be of value -- if the gas companies could come up with something to differentiate their gas from something else, they would and do. However, using the fuel system to deliver a compound for a specific job can accomplish something. Seafoam, for instance, will remove carbon deposits that gasoline detergents leave behind. You don't want to run it all the time, because it's unnecessary, but it does what it advertises. It's a more powerful engine cleaner than the detergents you'll find in even Top Tier gasolines, but does much the same job of removing the varnish and gum which traps carbon.

I would however point out that concentration is not really a good indication of whether or not a particular compound is effective. Household vinegar makes a good cleaner compared to water but has only 4% concentration. Though admittedly, for gasoline additives you're typically talking about mixing petroleum products into petroleum products, Seafoam is a 1 oz per gallon gas additive because it's meant to do a bigger job than the preventative cleaning of a gasoline's detergent. For regular use, a low concentration is fine -- but it's already in the gas, so why bother?