Interesting thread....
I have absolutely zero fear of heights whilst flying and like other posters have done static line parachuting with no probs - from standing on the wing of a DH Rapide.
Likewise tall buildings, cliffs etc are fine with me
However, I completely freak when faced with heights WITHIN a building, for example looking down the centre of a high staircase.
I once agreed to climb up to the whispering gallery in St Pauls. When I emerged at the circular walkway with a 200 ft plus void below the sensation of falling to my death was overwhelming. I froze with fear and my wife had to carefully prise my hands from the railings and guide me back to the stairs.