If you are talking about those supposed microchips as on ebay, yes they are a scam. All it is, is a resistor that you put on a sensor and it fools the computer into thinking something other than it really is and leans out the fuel.

Jet Chip is ok, but the same price as a tuner, say like Hypertech or Diablo Predator. The chip they have piggy backs onto the harness going into the ECU. One of teh biggest problem with these are, they are programmed what you tell them you have. Say an exhaust or CAI. Now if you add other factors that can cause leaning or the opposite, you can't change anything in the Chip. But with the tuners you can. I think you could also send the JetChip to them to get reflashed, but then there is extra cash you need to spend.