" ... so if the GPS sends me way wrong, which it has, I will hopefully catch on to it and re-navigate."
Although "GPS" is named a "positioning system", it really is just an accurate timing system. "Global timing system" would be a more apt name. GPS receivers, through a variety of clever techniques, determine the amount of time it takes for several signals transmitted from low orbiting satellites to propagate to your antenna, to within 10s of nanoseconds. GPSs don't "measure" position, they measure time differences. As a consequence of measuring time differences, position can be calculated*.
Why is this important to the discussion? Because "GPS" only measures propagation time of signals. Everything else is calculated. "GPS" isn't a car icon on a street map with soothing voice instructions to turn and follow a route. That is entirely a computer program. "GPS" isn't a handheld computer with a color display that shows your location plotted on a map with a track and waypoints. That is entirely a little handheld computer and a computer program.
In your example, "GPS" didn't send you the wrong way. A GPS receiver measured timing information of signals from space to within a few 10s of nanoseconds, and from this, it calculated your position accurately while you were travelling at a fairly high velocity. This in itself is a pretty awesome technological feat.
A computer program with a database of street map information, running on a small form factor computer with a little LCD display sent you the wrong way. GPS had nothing to do with it, except provide your location. Your location could have been provided by any number of ways: you could have input it directly, it could have attempted to triangulate your position from the stars, radio beacons, or from wifi networks (as apple ipod touchs do for example).
So, why the rant? This whole thread started with an article that GPS is making us dumber and that we cannot make mental maps, and that future generations are doomed. I just want to get it clear: measuring signals from space accurately within a few nanoseconds isn't a problem. Trusting little handheld computers running crappy software that attempt to read your mind and tell you where to go is the problem. GPS is great.
Saying that GPS sucks because the voice on your Tom Tom sent you the wrong way is like saying that magnetic navigation sucks in 200A.D. because paper maps didn't exist.
* I am not, and do not claim to be, a GPS expert. I am at best, a learned amateur. And am versed in PRN codes, how GPS timing is determined, and have written a couple of computer algorithms to turn pseudoranges into ECEF Earth-Centered-Earth-Fixed coordinates, and then into lat/lon positions, have done some dabbling in ionospheric/tropospheric correction terms, and have manually post-corrected said calculations with updated satellite ephemeris. As I said, not an expert, and I look forward to B.G. et al. correcting me for any discrepancies I may have made.