I have an '08 328i and it went out a little past 65,000 miles this April. The dealer replaced quite a bit and would have been an expensive repair had I not had the extended warranty. A coworker had his go out about 80,000ish on an '06 325i for another data point. Good luck, hope yours keeps cold for many miles to come. I feel sorry when I see people driving all windows down in this 95+ humid weather.
'08 E90 328: AW, beige, Light poplar, prem pkg, step auto, htd seats, xenon, i-drive, logic 7, 6FL Ipod connection, BMW performance exhaust & intake