I just got the recall notice - dated May 2012. It's Labelled "SCR Catylist, EGR Valve &/or DEF Mixer and ECU Software Flash"

Per the letter - BMW has determined that these parts may not be "robust enough" and after time may result in excessive NOx emissions along with illumination of SES Lamp.
It says that if the repair is not done the vehicle might fail an emission test. And in California it is mandatory.

They'll replace parts - if required. The repair will take one day.

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Current:
'10 335d Titanium Silver Premium, Nav, Ipod, Sat
'07 A3 Ibis White, Tint, 2t, DSG, Premium dual sunroof

Retired:
'69 VW Fastback
'73 MGB
'78 Camaro LT ttops
'80 VW Diesel rabbit
'81 Audi 4000 4E
'84 Audi 5000 5sp
'87 Audi 5000 auto
'90 Audi V8q
'92 Millenia
'01 Acura TL
'93 Miata b Candy Apple red, AC, Factory hardtop