My 2 cents on iDrive. I rented a BMW 1 series for about 2 months and it was equiped with iDrive. Intially I hated it but then it became bareable until when I finally turned in I got used to it and it was not so ok (not OMFG great mind but ok). idrive I found as something after one or two test drives or even a week you can get a good feel for. It took me 1.5 months to really appreciate it and I will be getting on my M3 if it is not standard equipment.
But I will agree with jo2k, HUD I think is a no brainer for anyone purchasing the M3.