BMW is the first automobile maker to integrate the iPod Out functionality of the iOS 4. This means that you'll be able to view your iPod's screens and menus right on your car's built-in display.
It might not seem like a huge deal, but there are benefits to such a setup:
The benefit of using the iPod Out connection is that it allows the interface to change and grow with the connected iPhone or iPod. If Apple adds, changes, or removes an iPod feature in the next revision, the connected BMW or Mini should immediately be able to reflect those changes.