A couple of things, I reckon jamair is spot on regarding SA. If I'm flying a VOR approach & there's an NDB as well, the NDB/ADF is great for maintaining orientation on the VOR approach. I think the yanks are approved to fly GPS overlays aren't they? Makes an NDB approach even safer (as long as it's runway aligned
)
Secondly, an ADF is horrendously expensive to install these days when you compare to glass. They are ripping NDB's out of the ground, so what is that saying? Goodbye NDB approaches I reckon.