Generally it works good in my car, better than some on past MB cars I've had. The ability to adjust the sensitivity is a great feature, and something that Mercedes is sorely lacking.

I usually find it wiping too much when it is misting and you are following cars. Even at the least sensitive, the thing was going like crazy. Yet, sometimes, I'm sitting waiting for it to wipe.

Wish the sensitivity was more than the 4 or so clicks you get... a dial with "infinite" adjustment like you get in cars with variable intermittents would be great....

Thanks for all the answers, seems like I am not the only one with this issue. Also talked to BMW Tech guy yesterday and he says the sensitivity of the rain sensor can be programmed via the 'Car Key Memory' function at the dealer.

Will try this the next time I am at the dealer...

mine too
 

I have noticed the rain sensor goofiness on my 2010 X5 diesel. My 2009 M3's sensor works exactly as expected (i.e., the same as the sensor in every BMW I've owned). The M3 is assembled in Germany while the X5 is assembled in the U.S., of course. Perhaps the mirror/sensor assembly supplier is different and the U.S. version doesn't work as well. Just a thought....

I've noticed same poor performance of rain sensor in 2009 X 35d. Not functioning nearly as well as previous BMW, 2002 530i.

Have noted issue of wipers taking off and wiping too fast, and sometimes not wiping enough.

I've had this happen a couple of times. I find doing a quick wipe - pushing the stalk down cures the problem.