I’ve just read a very very interesting document called “Linux Kernel Development — How Fast it is Going, Who is Doing It, What They are Doing, and Who is Sponsoring It: An August 2009 Update” by The Linux Foundation.
I found remarkable that there is this crazy David S. Miller, contributing so much code! I did not know this (because I deal with Linux seriously just since one year and one mainly reads about Linus.). Wikipedia says: “He was famously asked “Have you ever kissed a girl?” by Bryan Cantrill, a Solaris performance engineer, after Miller explained why Linux is substantially faster than Solaris.”
Furthermore, I think it’s interesing that Google itself does not produce that much code in comparison with other companies, but in Table 12, listing the code signoffs, they are on rank 2, behind Red Hat and before Novell.