I know this is an old thread, but I've been using John, Josh and Michelle Anderson at Bavarian Motorcars in Cumming since I bought my E92 in 2006. They are family-owned, love what they do, and have always been honest with me. Services aside from maintenance and repair include coding and aftermarket part installs aside from something like Dinan Shockware which requires an authorized Dinan software provider (like United BMW).
http://bmcofatlanta.com/