I sometimes get jealous of college kids today. When I was in school, computer networking was pretty much limited to BBSs and 2400 baud modems (although the college did have Internet access). I wonder what would have happened to me if open source had be prevalent in those days. All the time I spent drinking beer could have been turned into something more productive. (grin)
As Geoff points out, not only does working on open source projects give you something to put on your resumé, it allows you to make the connections to get that job in the first place.