A few years ago we had an aircraft that was mistakenly de-iced with hot water. The cabin crew noticed that icicles had formed as the aircraft taxiied to the holding point, informed the captain and perhaps saved the day. Failure to confirm that the airframe was clean was one of the many error made by the crew of the 737 that hit the Potomac bridge. After a de-ice I always have the wings checked by a flight deck crew member before take-off.