I've been using it to as full as possible extent for 16 months now.
I connect with both Sprint and Verizon 4G devices and it certainly functions very well no matter where I am.
Hopefully, people purchasing the newest models with Wi-Fi built in will get a year or two of connectivity included in their car payment, so it - at first - may seem free to them, but once they start getting charged for the wireless access by their mobile carrier I have some idea of the sticker shock awaiting them.
One gigabyte of data today costs about $10. I chose one of the carriers because they offered unlimited data at the time (after all, your new laptop needs at least a terabyte of storage!) Their coverage was disappointing as I explored back roads and parks, so I also ultimatelty bought the other one. Most months I pay about $120 between the two carriers to connect.
I keep it that "low" by never streaming anything I can avoid. One month, for example, I watched a total of 60 minutes of steaming video and my charges DOUBLED.
I see where Clear Channel is increasing their commitment to digital now. Ideally that will include HD and NextRadio, the digital audio services that will still be free for users to access.
The more drivers and passengers start having to pay for programming via 4G, I predict, the more they are going to appreciate the medium which serves their entertainment and info needs at no cost.