I contacted BMWUSA re the nav system as when I took delivery in Munich, the intersections, curve indications (in the HUD) were right on. I told them to have their programmer verify that the USA maps and the programming for the GPS were both using the same datum and spheroid, as mismatches can easily account for the errors we have. They called and said they'd have to forward it to Munich for research...never heard back. Called the guy once, got his voice-mail, but he never called back. Maybe it's time to try again!
There's no real excuse for the distance to turn indications to be off as much as they are. My phone, bike computer, and other gps devices I have all do better and they don't have a nice antenna on the roof with no obstructions, either.