Nope--issue came to a head after my insurance company wanted me to put a GPS tracker in my car to get lower rates.
So, I do without now. If I decide it's unavoidable, I'll buy an ancient clunker (preferably one with as little electronics in it as possible, think classic car).
Tons. I am going to say the majority. It is optional though. You usually get a discount just for signing up, then you get an additional discount for your driving
Progressive, Travels, Allstate, The Hartford...
They not only track your location, they track your speed, the amount of quick stops you make (an indication you are tailgating), and time of day (some times of day are more risky than others statistically), and how much you drive. People who drive at low risk times, don't drive very fast, don't make quick stops, and drive only a little bit get discounts. Usually you leave the device in your car for 6 months-1 year and your discount is forever. My insurance (Travelers) gives you a 30% discount max. You can also log on online and view all your stats.
You plug a device into your OBD-II port.
There are significant privacy issues at hand here. In one case, it can be argued that you shouldn't be tracked, in another case it can be argued that driving is extremely dangerous (more dangerous than many people assume) and every attempt should be made to make driving safer. Humans have already demonstrated that they will alter their driving behavior for financial gains.[1][2]
So, I do without now. If I decide it's unavoidable, I'll buy an ancient clunker (preferably one with as little electronics in it as possible, think classic car).