According to this guy, almost seventy five percent of Linux code is now written by paid / corporate developers.
The most striking aspect of the analysis, however, was where those lines of code originated from. 18% of contributions to the kernel were made without a specific corporate affiliation, suggesting true volunteer efforts. An additional 7% weren't classified. The remainder were from people working for specific companies in roles where developing that code was a major requirement. "75% of the code comes from people paid to do it," Corbet said.