Over the Christmas break, I've watched one of the basic powers of open source in action. Two employees from my Alfresco team did something that is largely impossible in the proprietary world:
They wrote integrations to third-party open-source software, the Apache Hadoop and Drupal projects. No contracts changed hands. No NDAs. Just code.
Open source, of course, is, and then sell them support or other add-on services or software. But it's also a fantastic way to collaborate with would-be partners. Not a single lawyer need get involved until the code is working, and then only to divvy up responsibilities and revenue, if you so choose.
Try the above integrations between two proprietary companies. First you get contacts from both companies (probably the executives, depending on the size of the company, because who has authority to make that kind of a decision?) to start talking about the integration. Then, before any real work happens, the lawyers need to get involved. (While at Novell, I had one of the most distressing experiences in my life trying to negotiate a partnership with Siebel. It's not an experience I'd wish on my worst enemy, much less a partner.) Further work will then need to be done to define the integration, marketing teams will need to get involved to define the go-to-market strategies and whatnot. And so on, until eventually code actually gets written, a year or so later.
With open source, you just need one guy and a week or two of downtime over Christmas. With proprietary software, you need a small army. Which do you think is the more efficient model?