Put me in the "Snake Oil" in the gas category, about cleaning the fuel system (including the injectors).
I personally include "FP Plus" (
http://www.lcdinc.com/products_fuel_power.php ) with just about every fill up. I first heard about that product on the "Bob Is the Oil Guy" forums, and it came highly recommended. My personal experience is that I tend to have just a little better power, and a little better FE, when I use the product. The effect isn't huge, but it is quite noticeable (to me). And while the product isn't cheap (almost $50/gal + shipping), you only use 1oz per 10gal of fuel (so it's not that hard to "cost justify the price, especially given the current gas prices).
And one of the other benefits of the product, is that it is supposed to gently clean the fuel system (including the injectors) while you drive. And while I have no personal way to judge that claim (unless I wanted to take the fuel system apart and look at it), others on the BITOG forum have reviewed those claims and seem to think they have some basis in fact. So it at least appears that my FI (my car has "throttle body injection", so I only have 1 (or was it 2?) fuel injector(s) for the entire engine) is constantly being "cleaned" by the fuel additive I am using.
NOTE:
The other benefits of "FP Plus" (such as its lubricating properties, and the slightly better fuel economy I get when using it), would cause it to "pay for itself" (especially with today's gas prices), even without the fuel system cleaning properties. So IMHO the fuel cleaning properties (including any cleaning it does with the injectors) is just "icing on the cake" as it were).