I believe the Westland Wasp http://en.wikipedia.org/wiki/Westland_Wasp uses negative collective pitch to enable the helicopter to stick to the deck until it able to be lashed to the deck. I think the Merlin also has that feature. Very useful in heavy seas.

It would also be good in a modified form for scuba divers. Depth, temperature, ascent rate, gas, bottom time, among other instrumentation would be very useful in a HUD. Perhaps 3D mapping as well for navigation around dive sites. We were actually discussing this on holiday in Dahab. Currently, wrist mounted dive computers are used for this sort of thing.