Right now I live in Virginia, but the fill up was in SC that I got the light on. Filled up with mid grade and light went out after 50 miles. This is what I was told to expect from local BMW dealer ( a good dealer at that) and is exactly the same behavior as our 2002 325. I do believe it is due to the new gas formulation. Could be that California gas was already oxygenated and maybe what I need to do is to reset my computer and have it learn the new formula, or maybe there is a California program that will solve this issue. I am noticing a drop in fuel efficiency with the mid grade. don't seem to see a lost in power, at least by the seat of the pants, however good that is. What I also do not know is: If alcohol is used as an octane boost, does that count in the 10% ethanol?
That is what my BMW dealer is saying is happening, the alcohol used to boost the octane pushed premium over the 10% figure.