It also happens when a group of runners stick their compasses next to each others to see which is right; they'll all try to point towards each other!
I think GPS watches are brilliant; I've been using my Forerunner for over 4 years now, both for getting an idea of how far I've gone and also for planning long runs as part of my Fellsman training.
It was extremely useful to be able to plan a 20-30 mile run in advance on a completely new area, just by drawing lines on Google Earth; took about 15-20 mins at most. Out on the run I could concentrate on following rather than finding my way and could maintain a much better pace. The 'return to start' feature is also very useful if you just want to run for a set distance; just press the button at halfway and it'll guide you home. Chances are you'll recognise most of it anyway.
I'd agree that compass and map skills are invaluable; gps devices are of little use in MM and other nav events when you get a map on the day. It would have been no use on the Fellsman 'cos the batteries don't last that long anyway!
But; don't knock gps devices if you haven't tried them (and I bet most of you haven't) they can be a very useful addition to your training.