Perhaps you've read my post "Manufacturers are Requesting Linux Drivers", but now there's a more in-depth and very interesting report. The newly published report by the Linux Foundation provides insight into the growth of the Linux kernel development community. It reveals that the entire code base has grown by 2.7 million lines over the past year while an average of 5.45 patches are accepted every hour, which is over 130 patches every day. The average kernel development cycle currently runs for 81 days - just under twelve weeks. A good geeky read.
You can download the report from the Linux Foundation website.