I obtained my '11 35d in June 2010. Around November or December it developed the same symptoms you are talking about. They deoderized it on my first service and told me something to the effect that it was bacteria buildup, it was my fault, BMW will deoderize the filter only once at their expense, and that I could make it not happen by not leaving it on recirculate all the time; I had to alternate between fresh air and recirc. I leave it on A, isn't that supposed to recirc sometimes and not others?

Anyhow, ALL BMWs don't do that because I owned my '03 E53 for 7yrs and NEVER had that problem.

On a side note, when I got my new X6 back from the body shop (1 week old; it was having the bumper repainted), the a/c smelled like french fries on startup! They deoderized the filter, but it still has remnants of the smell. I guess french fries is better than dirty socks.