Probably our favorite piece of crap-technology is the Tornado air-filter thing. The results it promises are a little-less than fantastic, as you can achieve a 1 to 2 MPG increase by just assuring the proper tire pressure level. The basically-useless piece of metal works by creating "unique airflow dynamics" to "atomize" the fuel allowing "better flame propagation" and "making the fuel-economy faeries fly out of your exhaust."
It's also a good way for someone you care about to waste like $50-$70 on something that you'd never, ever put anywhere near your engine. But hey, they quote John 3:16 on their website so they must be legit! Thank DamnElantra! for helping to prevent this POS from ending up under your tree.