writes "LWN.net did some data mining through the kernel source repository and put together an analysis of where the patches came from. It turns out that most kernel code is contributed by people paid to do the work — but the list of companies sponsoring kernel development has a surprise or two."
The article's conclusion: "The end result of all this is that a number of the widely-expressed opinions about kernel development turn out to be true. There really are thousands of developers — at least, almost 2,000 who put in at least one patch over the course of the last year. Linus Torvalds is directly responsible for a very small portion of the code which makes it into the kernel. Contemporary kernel development is spread out among a broad group of people, most of whom are paid for the work they do. Overall, the picture is of a broad-based and well-supported development community."