Aww...c'mon guys...all this "in theory" is nice...but my little GPS tells me exactly where I am and tells me what my margin of error might be.
Would I navigate without it...NO...Would I like additional input from radar...sure. In my recent trip up the Bay...I used both and NEEDED both but my eyeballs would have been absolutely useless. In ALL the last 10 years or so of using a GPS I have never once had cause to doubt the accuracy of my GPS within a few hundred feet. Most often I am within 10-30 feet of my waypoints.
As far as Loran goes...I used that too a long time ago and it was a good tool in its' day (and still excellent for REPLICATION of previous waypoints...i.e. fishermen!) but then the abacus was a good tool in its' day as well. (G)