While I dont have my E92 with idrive yet, I look forward to it. While the nav function is going to be nice, I mainly got it for its other functions. I like having control over the various car settings (entertainment and climate settings).
Joined with the ipod integration kit, I can hide my ipod in the car, and have greater use of it through the steering wheel controls and idrive controller.
If you are someone who enjoys gadgets, Im sure it would be a great addition to your car.