As AKViper says, US cars can run ethanol fine. Washington and Oregon have had ethanol blended gasoline for a while due to state tax advantages. Regards of component (ethanol, MTBE, ETBE, etc) the target is an oxygen content of 2.7% (I believe) in the finished fuel; this is to lean out the fuel-air mixture during warm-up when the engine is in open-loop (or when the choke is on.) Your volumetric miles per "gallon" should theoretically drop by the oxygen content since the oxygen doesn't provide energy.
While it does pick up water (a good thing) it is also good at picking up other things (rust, scale, dead leaves and bugs) from your gas tank and the service station tank. Critical period is when you or the service station first switches as most of the "cleaning out" is done quickly. If you have any fuel issues, you might want to replace fuel filters first.
Ethanol also has a high latent heat of vaporization. That is why it feels "cold" on your skin - it is taking heat from your body to turn into a vapor. Ethanol does the same in your engine, it takes heat from the intake charge. In a fully warmed up engine, this may allow a denser mixture to get into the combustion chamber. In an engine still warming up, it may cause a little stumble or hesitation, since the fuel doesn't vaporize as well. Not so much a problem with fuel injected engines, but very noticeable in carbureted engines.
