Yahoo Autos reports that 96 percent of new cars sold have data recorders, or "black boxes," that reveal the details of a vehicle before an accident.
Source: Yep, Your Car Is Definitely Spying On You, Ford Exec Reminds Us | HuffPost

Nearly 100% of cars on the market include wireless technologies that could pose vulnerabilities to hacking or privacy intrusions.
Source: Cars Are Delivering Tons Of Driving Data To Manufacturers With Minimal Security And Even Less Transparency | Techdirt

A friend recently told me that my insurance company could monitor my driving habits from my 2016 Subaru's StarLink system.
And that most cars are being monitored by the manufacturer.

It turns out that even though my display says "StarLink" when I start up my 2016 Subaru, it is not equipped with StarLink hardware or software and cannot communicate remotely.

From what I could find less than 5% of cars on the road as of 2016 had these remote access systems enabled. I couldn't find any hard data on the actual number.

In 2011, OnStar said that it would start retaining all the information collected by the GPS and internal system so that it could be sold to third parties (possibly insurance companies).
A few weeks later, after outcry from subscribers and privacy advocate groups, OnStar reversed the decision to continue collecting information from unsubscribed units.
Source: OnStar - Wikipedia

OnStar was formed in 1996 as a collaboration between GM, Electronic Data Systems and Hughes Electronics Corporation. From 2002 to 2006, OnStar service was available on vehicles produced by Acura, Isuzu, Subaru and Volkswagen

In its document of privacy practices, OnStar states that it is not possible for them to listen to or monitor conversations in a car without the knowledge of the occupant. The hardware is designed so that when an advisor calls into a car, a light flashes, a ring tone is heard, and the radio will mute.

In July 2011 a hacker introduced a device that could interpose itself between the vehicle's OnStar link and the driver's OnStar RemoteLink app. By August OnStar released an upgrade to block it.

The Rise of OnStar - IHS Technology OnStar, the automotive telematics communications system now installed in all new General Motors vehicles, is set to grow steadily during the next few years as renewal rates for the service push total subscribers to 7.9 million by the end of 2017, up from 5.1 million in 2010, according to new research from IHS

OnStar App Stats, Usage And More | GM Authority In its various versions, RemoteLink currently has 1.3 million total active users, and here are some more stats that you might not have seen.

Overall, there were an estimated 263.6 million registered passenger vehicles in the United States in 2015.

GM Cuts OnStar Free Trial Period For New Cars | GM Authority New York Daily News reports GM has sliced the free trial period from a generous six months to just three months.

Even if the vehicle is OnStar equipped, no OnStar services are available until the system is activated.

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