What's really hard for me to understand is why anyone who's not involved in a business or personal situation that requires driving constantly to new places would want one. I find them annoying and often wrong. If you're a "soccer mom" its hard to imagine really needing one... does the soccer field move every day? Airplanes have them as well - why? Hopefully the pilot of your average commercial airliner knows where he is going...
(Personally my strategy is to always plot my path on some mapping site, often Google, before I travel to somewhere new. I can use it to not only survey the area around the destination but, with the street view feature, see what landmarks I might need. I also use my iPhone mapping app. But the bottom line is to always know where I am going before I leave.)
There are also problems with GPS systems. They can be jammed (purposefully or by accident), they can be wrong, and they can be spoofed.
Jamming is fairly easy. GPS operates at 1.57542 GHz (L1 signal) and 1.2276 GHz (L2 signal) - so anything disrupting these frequencies will jam it. Some commercial systems, for example the proposed LightSquared 4G terrestrial-satellite-based service, supposedly disrupts GPS for aviation.
Secondly, most civilian applications of GPS require a corresponding map that the GPS signals create a correlation with, i.e., the GPS signal places you somewhere on the surface of the earth - the mapping software takes that position and shows you a street, for example.
The maps can be wrong. And because the typical car GPS is giving you directions verbally in real time a mistake in the map can cause you to be directed into something bad - a wall, over a cliff, into on coming traffic, etc.
Then there is spoofing.
The idea behind spoofing is to provide a GPS receive a "fake" GPS satellite signal that tells the receiver that it is located somewhere where its not.
The basic L1/L2 satellite signals are coming in from space and are relatively weak so, for example, an aircraft flying over a receiver could send out stronger signals with different information that would overpower the satellite GPS signals.
The GPS receiver would not be able to tell the difference (as they do not rely on signal strength - only signal timing and content).
According to this Information Week article this is what was used by Iran to capture a US drone.
This is something that apparently the US military has known about as a potential problem for many years and various GPS issues are known to be potential counter-threats to US interests. (See this 2003 paper and this UK news article.)
(Gee, let's build a multi-billion dollar system for the military and then give away access to everyone so it can be circumvented - only let's do this after we build our entire military infrastructure around it. Don't believe me, see this from msnbc.com.)
Now this should not be happening - and in particular no Iranians should be spoofing the GPS.
The reason, because when GPS was first envisioned and created and run, it had heavy encryption.
The L1/L2 satellite signals from space were encoded so that no one could duplicate them without the proper key. Thus military systems needing GPS could rely on the encrypted signals which enemies could not forge. Somewhere along the line this was either removed or relaxed - or, worse yet - the idiots building the US drones didn't use it.
I cannot tell which is the case with the captured Iranian drone.
One would sincerely hope that military drones used encrypted GPS signals.
But if the reports are true it was not... its hard to say what the truth is here. There is all sorts of stuff flying around the internet related to it (see this, and this, and video below).
There are other possibilities.
For example, depending the the speed of the drone it could simply be snatched out of the air with some sort of fast helicopter and a trapping device (net, cables, something).
I think that part of the problem is that the US is very arrogant about their technology, and, when folks like those in Iran figure it out, they pretend they didn't.
So I smell cover-up at some level. Whether the drone self-destructed failed or it was simply a bad design or whether the GPS was spoofed or whether the RSA encrypted military GPS was hacked.
There seems to be some belief that because the Iranians are not like us they are stupid.
This is a dangerous assumption.
The capture of the drone should be a wake-up call...