Great thread. Even more uninformed rubbish than usual.
As it happens I know quite a lot about GPS accuracy (I have spent the last two years deploying GPS in a non-aviation application and actually testing the accuracy of various commercial units both statically and dynamically) but I won't bore anyone here with what I have found out as it would spoil this thread....
Suffice to say, the problem will almost always be with the operator and not the kit - as it was last time I dialed '190' into my VOR instead of '170' and ended up somewhere I did not mean to go.....