This video is from a man who thinks his harddrive magnets are doing all the work. I thought this was humorous because the simple terrain, weather, or even the guys foot could be the cause to his mpg gain. Plus I am not so sure the gauge he is referring to is trustworthy.
another thing to remember. I knew a guy about 8 years ago who was selling blankets/pillows with magnets in them. They were the cureall for all of your physical ailments. The miracle cure.
Magnets have been the mystery cure for so many things over the years, so it's really no shock that they would suddenly be used to give you better mileage.
In reality, the claims that magnets can give you better mileage is no different than the claim that they'll realign your energy flow and cure cancer.
Concerning the video, remember that a true experiment will use a double-blind study, where neither the experimenter nor the subject know if the conditions have changed. in this instance, the experimenter and the subject were the same person, and he knew that the magnets were added. This, by itself, invalidates the results.
If you want to really find out if it works, put the magnets on your wife's fuel line without telling her. Ask her to track her fuel consumption. Over a few months, you could probably get a feeling for if the magnets really had an effect. Oh, while you're at it, also keep track of the temperature, the duration of trips, etc. just so you can rule out confounding factors.
Had a dead HD laying around and taped the magnets to the fuel inlet line (before the fuel distrubutor) on my car, and haven't seen any change from it...other than some wasted time dismantling the drive and 6" of duct tape. I suppose once I get the car "stabilized" I will pull them off and see if I suddenly loose FE.
McIntyre's First Law: "Under the right circumstances, anything I tell you may be wrong."
O'Brien's First Corollary to McIntyre's First Law: "I don't know what the right circumstances are, either."