I've had the same scenario as PurpleTT where the idrive crashes randomly. I can usually tell it's about to crash as the music I'm listening to will start to go crackly a few minutes before it crashes.
I took mine into the dealership a couple of weeks ago and apparently BMW Technical know about this problem and are working on a fix as they believe it to be software related. I'm not holding my breath on an easy fix mind you....
Soon to Depart
335d XDrive M Sport Moonstone
with Black Merino Leather interior
On order: M5 Singapore Grey with Sakhir Orange interior