on my last car i avoided ethanol gas like the plague because my mileage would drop badly.
on an extended drive (360 miles), mostly interstate, i had to fill up with 10% ethanol, and my mileage actually was up 1 or 2 mpg higher than normal. imagine my surprise. i haven't tried it since, and my mileage has repeated the all time high a couple of times.
i have a 2002 impreza 2.5rs, 11,000+ miles.
my biggest long term concern with ethanol is the reaction it has with seals and gaskets. most fuel systems are designed to handle ethanol today, but it wasn't that long ago that fuel system components could be eaten up by ethanol or other high alcohol fuels.