It is not just i-Drive, it is the concept of controlling main system functions from a central display. Lexus, Infiniti, BMW are all starting to do it.
I think long term it will ruin the heritage of the vehicles.
Think about it, you buy a 645ci with i-Drive for 80k. In 10-20 years the car will be worth let's say 8-10k. The i-Drive is broken thereby rendering the A/C, Heat, Audio, and Nav useless. The cost to repair will likely be at least 3-5k assuming you can even get parts. There will be no way to put in after market parts. So I think what will happend is the cars will become step children.
The whole idea of a computer screen in a car is fairly new. There have not been any long term tests to suggest how reliable the computers and screens will be. However, in corporate america, we replace computers every 2-3 years and they are not getting bounced around on the road or subjected to extreme heat and cold.
Also, I have read several articles on how the Nav systems are just a scam to increase dealer profit another 5%. The average Nav system costs about 2k. Assuming you keep the car for four years, that is $500 per year for the Nav. If you look up an address once per week, (this is average for most users), each lookup costs you about $10. Most people ignore their Nav after a few months because it is more of a Novelty. The ones that really need them are motorhomes, cab/limo drivers, ambulance/fire.
I work for a large telecommunications company. Although I cannot go into to specifics, the technology coming out on cell phones and PDAs will blow away the car nav and all for approx $100 bucks. And you will be able to walk down the street or ride a bike and use it so you won't be tied to a car.
Maps change all the time, the map in your car is outdated as soon as the DVD is burned. Realtime access to real, accurate data is the way of the future. Not some auto maker deciding to put a cell phone or nav system in a car and then finally getting it to market 3 years laters where it is already obsolete.