aterpster, don't confuse probability with overall accuracy. GPS navigation is perfectly fine for terrain avoidance as long as one gives a wide-enough margin to allow for the inherent inaccuracy. One does not buzz a peak in IMC with a 50ft clearance if one can avoid it. On the other hand, that 50 feet will make the difference between green and grey on a landing.
I use GPS waypoints in the Sahara regularly, and it is common occurrence to find marked points be off the actual position by 5-10 metres on a return years later, and that is without the altitude component.
That being said, me too would welcome a return to the thread topic.