Everyone always forgets to look at the total package when considering an OEM navigation system. Being in IT for way too many years, and having tested and designed user interfaces (UI), there are always trade-offs weighed between the user, the application, and hardware. This is why the iPhone/iPod Touch has won such praise… a very well balanced design.
Sure, from a pure software view, the iDrive UI could be changed to make it more intuitive, but this would require more buttons and/or touch capabilities. Just look at the center stack and console of any Audi with nav (below)… way to cluttered in my opinion. And from the driver’s perspective, touch just doesn’t make sense (i.e. dangerous) which is why most OEM navs have limited input while driving (a big positive for iDrive!).
In my 2008 coupe, I don’t see speed being an issue and it has never locked up.