I paid a ridiculously high price (IMHO) at a Quick Lane at a local Ford dealership for fuel system cleaning. They recommend doing it every 30,000 miles. They say that they disconnect some fuel lines and run some strong solution through the injectors and other motor parts. This is probably the best way to clean injectors. The car seems to run slightly better. During the last two fill ups (the only after that service) it seems like the car started getting 1mpg more than it used to (of course, this may not be statistically significant, or I just was using less AC this time of year). The price was $159 and this was a special for me because I told that this is the price I heard before and won't pay any more (they agreed).