Holy crap your car is smoking pretty seriously, it could be coolant, a seal leak of some type, or worst case a blown head gasket. Maybe just condensation. Tough to say but i'd get that checked out asap. Mileage? How much boost have you been running? Head gaskets don't let go on our cars all that often, just reading around I only see it happen to people running extremely aggressive boost for the most part.
E88 N54 Alpinweiss/Coral Red/Motiv HTA 3586r Tial .82AR/Motiv Port Fuel/Meisterschaft Race/Berk Resonated/ER CP/Synapse/VRSF FMIC/Rob Beck PCV Valve + Cap/ST Coilovers/M3 FCA + Tension Rods/M3 Subframe Bushings/M3 FSB/AA Strutbrace/DINAN Camber Plates/Apex ARC-8/Project Kics/VAC Hubs/Rogue Transmission Mounts/Alpina TCU Flash/Icarbon/#Tee CF Stuff/Kerscher/BMW Performance