I believe I heard about a 4 x DU fail due to a wiring loom issue behind the instrument panel somewhere in Scandinavia. Fortunately the crew was just coming out of the cloud as it happened. So, its not a completely far-fetched scenario! I like to get students to do at least one approach on ESIS during the training - it helps to give confidence in their operation of the helicopter if they know they can get home using just one small part of the equipment!
Crab - you are right: most dangerous button on the helicopter! Trouble is, it is a certification requirement - (probably again a throwback to stoneage AFCS). Most experienced pilots say they have accidentally pushed it, or been on board when someone else has accidentally pushed it at least once! ......So, guess where the button is on the new 169??? Answers on a postcard!