According to Spolsky, he'd take the CS degree. Since he is an internet celebrity, people will use him as a credible source to justify their hiring reasons. Also, the HR filters don't really care what open source you've done in your spare time. They won't have much knowledge on it. They will understand what a Harvard, MIT, Stanford, Yale graduate can bring to the table. But your contribution to Apache won't mean much to the filterer.

Now, having personal contact and a network throws all of this out the window. I don't have a CS degree, I've never gotten a job offer without someone having personally reviewed my application. A friend in HR says they use software that looks for competitors (aka work experience), degrees, languages in that order.