I can see why a GPS approach could end in disaster if the pilot was not fully conversant with the way the "box" works it has taken me a few hours of reading the manual and playing with the box on the take home simulator and I am now happy to do a GPS approach in VMC.
The whole GPS thing has to be better than the ADF but and it is a big but..........the aircraft has to meet the GPS approach TSO, this I suspect will be the downfall of a lot of aicraft GPS instalations as most owners seem to pennypinch and dont get the full TSO instalation done.