Well, I haven't driven the new 7er, but I tested the I-Drive at the dealer. Actually, I-Drive is only used for the things you use not that often, there are still other buttons for the functions you use very often (e.g. on the steering wheel) while you drive, like rising or lowering the volume of the radio. And of course you have voice control for some functions, say "Play CD" and it plays your cd. With the I-Drive you have vertical menus, push the i-drive into the direction of the menu you want, press it, then select/change the things you want by pushing into their direction and press it again. The display of the I-Drive is also in a very good position, very high, so that you can look at it easily.
Here's a picture of one of those menus:
I think having I-Drive is better than having hundreds of different buttons.
The worst thing about I-Drive is that you don't have a gear stick anymore, just that damn automatic-stick behind the steering wheel