I don't have the feature on my M3 but the X3 loaner i had recently did have this feature and i think it's completely retarded.
What are the actual gas savings? I read like 1mpg? You can easily get that from just changing your driving habits slightly
Sure, they say that it's a new starter design and they engineered it so the battery and starter doesn't get damaged.... but what about the rest of the power train? I could be wrong but I don't see how turning something on and off repeatedly can be good.