I have no idea how old the systems are behind this data point but it seems relevant nonetheless: there are apparently 200-300 billion lines of COBOL still in production: http://www.enterpriseinnovation.net/content/how-should-gover...

This showed up here a while back and is also an interesting read: http://fosspatents.blogspot.com/2010/08/western-civilization...

Sometimes in all my eagerness to keep up and constantly re-educate myself on a daily basis I forget that there are still a lot of very, very old systems out there.