It turns out, as per Mr. Alexy's research, that open source can have a salubrious effect on one's stock price, but only if done right:
Companies saw their stock price rise if they met one crucial condition: explaining how they expected their open strategy to bring in short-term revenue. Companies that clearly communicated a short-term revenue model saw an average stock-price increase of 1.6 percent. Companies that didn't saw an average decline of 1.6 percent. This means companies can't rely on vague long-term assurances.
Ironically, this betrays a woefully naive view of open source by the market. Open source is a marathon, not a sprint. It's not a quick fix for any business.
In other words, the very thing that the companies most need to do (i.e., take a long-term view of open source's benefits for their businesses) is the thing most likely to punish them in the market. Who said markets are rational?