The only thing I'd trust a GPS for routing me to would be something like "The Joe's Crab Shack restaurant in San Diego". And then, only if I were in San Diego to start with. I sometimes use a GPS to suppliment maps when on the highway (predicting time-of-arrival, etc.), but the GPS suppliments the maps, not the other way around. And just like I wouldn't follow a map onto a backwoods snowpacked road, I wouldn't follow a GPS there either.

In the backcountry, for hiking, GPS's can be great for finding out where you are, but again that should suppliment, not replace, your knowledge of determining your position by other means.