Oliver Alexy of Technische Universitat Munchen (TUM) Business School has written an interesting paper titled "Putting a Value on Openness: The Effect of Product Source Code Releases on the Market Value of Firms." The research traces the impact of open source on company market valuations from January 1, 1999, to April 30, 2007. The research is hampered somewhat by a lack of private-company data, but it still offers up some useful conclusions.