On my 4DR 3.2 M3 that I had, I used to get around 7-8 Km/l in town driving, and that was driving really nice. Open road it climbed to around 10-11 Km/l at around 120 Km/h with cruse control engaged on a straight road. These cars are not really light on juice in town driving, and short distances doesn't help either. Open road, yes !!
But like they said, only one way to drive these cars. Drive it like you stole it :thumbs:, and don't complain about consumption.