Interesting that of the cabin crew reporting. I was taking an A330 out of a northern german airfield. Their was some ice over the collector tanks (Inboard aft of the wing) this is perfectly allowable. However it was reported to me by a concerned cabin crew member. Company policy to take cabin crew reports seriously, so I got the aircraft de-iced so as not to undermine cabin crews confidence in reporting. Cost the company a "pretty penny" but hey how far do you take training. Yes I know I could of just told them it was OK, but suspect that would have undermined their confidence and would have resulted in them writing it up, which I suspect their managers would have taken further, with all that would have entailed.