I've been using TC-W3 marine oil in my gas for a couple of years now, it's pretty cheap at $13/gallon at Walmart and you use around a 1:500 ratio, roughly 1 oz per 4 gallons.
Found this thread a couple years back and decided to give it a try. I used to use MMO several years ago and always liked the results but the WC-W3 has me sold.
http://www.ls1.com/forums/f48/been-testing-oil-91206/
There are quite a few threads on the web that discuss this as a fuel additive. I understand it became more popular after the ethanol blends came out.
No problems after 10K+ miles in my Audi or my STS-V. Only put a few thousand miles a year on the Escalade so I won't throw that one in the mix. I drive 30K miles a year on average so a gallon of this stuff lasts about 1.5 - 2 months. Not bad for $13.