Put me in the "it's horse$#|+" category as well. Motor oil is a balanced blend of ingredients to achieve the various goals of the engineers that designed the engine and the regulations governing its performance, etc. Adding something to it, unless it's another similarly-formulated motor oil product, by definition throws off the balance. You might gain in one particular area that can be easily demonstrated at a shyster/huckster convention like a fair or a trade show or about 99% of what's on TV, but if they tested all the aspects of the motor oil before and after adding the product, which they can't possibly do in the few seconds they have to get your attention, the end result would almost certainly show serious deficiencies introduced as a direct result of adding their product. And, as has already come up in a bajillion other such testimonial threads, if the product really had benefits like those described, why wouldn't the manufacturer stick it in there and use it as a marketing advantage? This isn't the bad old days of engine design where a glaring inadequacy like a massive intake restriction or an ingredient missing from motor oil is going to pass muster with the buying public. Competition is too fierce in the industry for any of them to let such a cheap advantage pass them by. This phenomenon will only become stronger as the required fuel economy averages continue to go up to approximately double their current values in 11 years time. Why do all that research, development, and engineering when the required mileage and HP are in this bottle for $19.95?
If you used all the various products for oil, intake stuff, gas additives, and they all had the advantages claimed, your car would last forever and you'd only go to the gas station to drain the excess gas out of the tank because you'd be getting about 930% better gas mileage.
It is true, however, that a K&N sticker gets you 20 more HP and 31 more lb/ft torque.