Yes, they do adjust timing and fueling accordingly based on knock- pretty much all EFI cars do, but retarding the timing to compensate for lower octane will have an adverse affect on performance.

It is not "that important" as in it will blow up if the wrong fuel is used, but it is not doing anything for performance. I just know enough about cars to know that I would not run anything less in a 10:1 compression motor no matter what the ECU will do. It will not hurt anything, but for the small price difference, I will not lose performance over something so simple. If I were taking a long trip or something on the highway where I wouldn't be driving "spiritedly", then I would probably just fill it with regular to save some $$$ over the course of the drive (like from NY to FL or something). I just will not use it in my daily driving.

Joe