I recently learned that the energy cost to produce ethanol for cars is much less than the energy benefit, contrary to popular belief. (In fact, the reverse is true for gasoline, which has not seemed to prevent our huge use of gasoline.) Further, if we are at or near "peak oil," the price of gasoline is never going to come down and stay down. Biofuels (not hydrogen nor hybrids IMHO) are our only hope if we are to stop sending boatloads of money to people who would destroy us.
So I have looked at the pros and cons of using E85 (85% ethanol, 15% gasoline), which has recently become available in Albany, NY, near where I live. It seems that Subarus love ethanol, which is close to a racing fuel for them. The energy density of ethanol is lower than that of gasoline, but what counts is miles per dollar, not miles per gallon. (Stories of corrosion damage by ethanol are apparently not true for modern cars, in which neoprene has replaced lots of the rubber that used to be used. Methanol is a different story.)
One can buy kits to convert any fuel-injected car for ethanol/gasoline use in any proportion. The kits are supposed to fool your ECU into enriching the mixtures without lighting up the Check Engine light. One intrepid WRX user on another forum just replaced his fuel injectors with others of a greater nozzle diameter, as I understand it.
What happens if one fills up with E85 and does nothing to "convert" his car? I imagine that performance would suffer somewhat, but would the car run OK although somewhat lean? Is it really necessary to convert?