The OC Register had an article yesterday that mentions how an injured mountain biker was rescued thanks to his trusty GPS and cell phone. Devon Kemp was mountain biking on the San Juan trail when he was thrown from his bike. Quick thinking led his riding partner to call 911 on his cell phone and he was able to give rescuers their EXACT location using the GPS. A helicopter was there within minutes for the rescue.
Of course the lucky part here is that the guys were able to get cell phone coverage on the trail. While your GPS will work anywhere on the planet, cell phone towers are few and far between in most backcountry areas. Another thing to keep in mind is that most recreational GPS units (like the Garmin Edge and low end eTrex units) don’t have built in basemaps so you won’t be able to use those to navigate to the nearest road or town. If you’ve been keeping track data on your route or if you marked the trailhead with a waypoint you can at least use the GPS to retrace your steps.