Michael Sauers posted a great presentation introducing the ideas and practical aspects of open source software, with examples from desktop applications to Linux to server software and library examples. He explains the concepts in a way that's highly suitable for non-techies. If you're curious about OSS I recommend it.
I like that Michael discusses the pros and cons in pretty honest terms here, and his point of view is (to borrow from Karin Dalziel) "OS agnostic" in a sensible way. I'd have liked to hear a little more about library-specific applications, but cramming that into a 30-minute introductory presentation would have been tough.
It's a half-hour audio presentation and his slides are available as well (though the audio stands fine on its own).
(And another example of Twitter is becoming more useful to me: if I hadn't been following Michael on Twitter I probably would have missed this.)