An interesting debate so far.
Just to concentrate the mind:
Zone infringments have been responsible for the vast majority of the serious breaches in safety in NATS airspace so far this year. Those people who seem to accept that infringements are OK (and that cutting the corner INSIDE CAS is also OK...) might not be so relaxed about it if their nearest and dearest were aboard one of the civil airliners which missed a zone infringer 'by providence' (i.e. no-one was able to take effective action to keep them apart).
I have on occasion been one of those 'right down the edge of CAS' people, thinking that it was my right to exercise my freedom in the open FIR. No longer so. Use whatever you can (GPS, Eyeball, VOR/DME) to be sure of your position, but give yourself a buffer in case of wind changes, lack of attention etc. As some have already said, if you are spending all your time concentrating on following a line on a GPS or CDI or track crawling, what are you doing to stop yourself flying into another aircraft?