Thinking about Open Source

I've been reading a lot of books/articles/research papers about open source recently, and (perhaps naturally) one frequent question is why developers participate in open source. The question is typically posed something like "What motivates developers to contribute time and code to open source?" or "Why do they give away their work for free?" Within the scope of such studies, a variety of motives and incentives is kept in the foreground.

But then, perhaps as a simplifying assumption, variation in motives and incentives is ignored when studying projects themselves, especially large (sets of) projects like Eclipse.org, Apache, or Linux. Let's ask the question: Why do companies contribute to Eclipse.org? And let's deal with the facts of variation and change of motivation and incentives over time. I think that would be very interesting to look at...