When I bought my M3, I opted out of the navi and iDrive so that I can go the route you just did. Very nice! Frankly, I have found that no factory-based navigation system worked as good as a cheap portable Garmin.
Great choice and execution, but just wondering what went into your choice of Eclipse versus Pioneer or Kenwood (with the Garmin-based navi)? With a few weeks of playing around with it, any further comments you wanted to add?