I actually had a very bad experience today with the nav system. Myself, my wife and our two kids (2 and 4 years old) were going to go hiking at a short trail near a waterfall in the North GA mountains. We were headed to the trailhead, and it turned out the access road was a pretty bumpy dirt road. We ended up turning around after about 1/2 mile and went back out to the paved road to find another hiking option.
We got to the paved road which had easy access back to the major roads that lead back to Atlanta and to the various towns in North GA, and then tried to pull up directions to Amicalola Falls on Waze. We couldn't get a signal on the cell phones where we were (common in many parts of North GA), but the Tesla was still getting enough of a signal for nav to work.
We entered our destination (Amicalola Falls State Park) and it came right up with what looked like a reasonable 20 minute drive on the nav system. I had no way of double-checking the route since we couldn't get a cell signal.
Below is the route it gave us from Google maps (note it said 20 minute drive on the nav system):
Here is the route it should have given us, which was both shorter and on completely paved and well-maintained roads:
The road we took ended up being an extremely rocky mountain road that you really needed a raised 4x4 to traverse. We spent 2 whole hours crawling along at 3 - 5 mph over extremely rough terrain. My wife and I were afraid we were going to end up stranded in the woods with no cell signal. I still can't believe we somehow made it through. I am very glad I had the air suspension which I set on "very high" and all wheel drive which helped pull us through some mud pits and up some very rocky inclines.
I ended up scraping the bottom of the car a few times, but luckily it looks like only a few scratches on the scrub plate and bottom of the front spoiler. It was really a miracle we made it through.
Here is a 3 minute clip from my dashboard cam that shows what the road was like. We were stuck on this kind of road for 2 hours.
https://dl.dropboxusercontent.com/u/4480164/videos/2017-02-26-12-36-25.MOV
At the end of the day, I know it is ultimately my fault for following the nav, but I really didn't think any nav system would take a vehicle on a road like this one. It really wasn't a road at all.