AFAIK we don't have any components in the fuel system which will be attacked. We've had 5% Ethanol in fuel for a while so I'd have expected to notice any problems by now.
The main difference is that the cars will run a bit weaker as Ethanol has a lower air ratio for stoich. I doubt it will be a problem for standard cars (closed loop while cruising and very rich anyway on boost) but may cause problems with aftermarket / piggyback ECU's set a bit too close to the edge.