Bike-riding definitely saves gas, and is good for the waistline, too! Boulder, CO is one of the leanest and fittest cities in the US, and nearly everyone there rides bikes. However, with today's sprawl, it's not always (or often) possible to bike to work or school. Put pressure on your city planners to reduce sprawl, increase public transportation (in an intelligent manner, for once!), and make non-car commuting more convenient!

As for octane rating, it won't make a difference for regular cars, quite right, and if the manufacturer says to use 87 as a minimum, then using a higher rating will almost always be just a waste. (My dad's old 1990 Buick Estate Wagon is an exception, it was supposed to run on 87 but would knock like crazy unless he used 89. That was some annoying design flaw.) If your manufacturer specifies 91 or higher for your sports car, though, you should probably follow it since the tuned engine will likely knock or ping with the lower octane. Cars with turbos should definitely follow the manufacturer ratings, since they're most sensitive to knocking. I should also point out that using a lower-rated gas than specified by the manufacturer may void your warranty if you have engine problems, as the dealer may use the fact that you didn't follow the manufacturer requirements to claim that you were negligent (whether or not that is true). If you're out of warranty, no worries there.