No problems with mine. Bought it with 29k on the odo. At 33k, it had trouble coming out of the trunk, dealer adjusted it and its been problem free for the past 7k miles.
It is not recommended to take the convertible through a high pressure car wash. I do it and haven't had any issues (unless the guy drying the car gets it before I see it). Its not supposed to leak during rain.
Coming from a soft top, I prefer this hard top as it isolates road/wind noise from the cabin better than that of the soft top.
2009 335i 6MT M-Sport AW/CR Convertible & Border Collie