Depends which bit of the UK your in how often it gets jammed
Last year it was brought up in parlament that the fishermen were getting pissed off that the days they could put to sea they couldn't find the fishing grounds due to jamming. The mil had to stop jamming I think. It was in the Scotsman or the Herald.
Of course we use it everyday and flying an auld heap with 25 year old wiring we have more chance of chaffed wires and other gremilins taking it out.
Its the other associated skills which are lost as well. If I want a center fix and I am heading towards an airport I don't need to plug it in the box I just use the 1 in 60 rule and a bit of geometry. Takes under a second to work out the heading.
GPS is very good and I use it everyday. If it goes tits up, it really isn't a hassell we still get to where we are going safely with very little fuss. The magenta line borgs struggle and usually end up cacking themselves. Even had one who thought loosing the GPS was worthy of a mayday.