"Ford’s 2005 models contain between two and three million lines of code. Current 2007/2008 vehicles have an average of six million lines of code. The company is expecting about 10 million lines of code in its vehicles in 2010." http://www.plm.automation.siemens.com/en_sg/about_us/success...

Although it's an unfair comparison if you're counting all the dozens of subsystems in the car, mostly developed by third parties, but not counting the OS kernel, full MySQL source, libraries, etc. used by Facebook & Twitter.