In combustion, ethanol provides less energy than gasoline, resulting in reduced fuel economy. When ethanol burns inside the engine, it tends to form a weaker mixture that may casue misfire, rough idle and cold start issues in your vehicle. In addition, engine components may deteriorate over time when in contact with ethanol.
Originally Posted by apecush
What reasons do you have other than hearsay not to use it?
The above quote is an excerpt from BMW themselves, feel free to click here
to read the bulletin in its entirety.