This trend in turn has led to a new debate, says 451 Group analyst Jay Lyman.

"Today's open source vs. proprietary software debates typically center not on which model is better, as I think there is some general agreement that both have their place," he says. "Instead, today's discussion centers on what is open source or not."

Amazon's Elastic Compute Cloud and other public cloud services are largely built with open-source components like MySQL, JBoss, Tomcat, Xen and Linux. "But are they open source? Most people would rightly say they are not," Lyman says. "Nevertheless, all of the underlying pieces are open source."

"It used to be pretty clearly defined whether a vendor or product was open source, but as we've seen the largest vendors in the industry -- all of them -- embrace and integrate with open source software, those lines of definition have bled together," he adds.