It's "free forever," but you've overstayed your welcome.
With difficult financial reports and questions regarding its treatment of employees, it seems Tesla now has a new problem on its hands: it really pissed off some of its customers with a letter to some Model S owners. Apparently, the company thinks that some of these drivers are overstaying their welcome, using the supercharging stations too often or for too long. According to a thread on Tesla Motors Club, an owners' forum, some customers have recently gotten a gently-worded request to reexamine their use of supercharging stations.
As a frequent user of local Superchargers we ask that you decrease your local Supercharging and promptly move your Model S once charging is complete. Doing so ensures a better experience for the whole Tesla ownership community and allows Supercharger resources to be available for those who need them most." This may seem like a legitimate request, but some recipients didn't think so. Some wrote that they'd only visited charging stations a number of times, while others said the closest station was 100 miles from their homes. Is Tesla cutting corners on the backs of its customers, or should some guests just get a better feel for when their free dinner has been cleared?