Obviously, this isn't breaking news. I saw this set of figures from Ohloh this morning. If you're not familiar with it, Ohlog is a website that tracks information about Open Source development projects by scanning the major OSS sites like SourceForge. According to them, in the last 5 years there were:
146,996,128 lines of code committed by 10,604 people to Java OSS projects.
22,800,806 lines of code committed by 1,817 people to C# OSS projects (The numbers for VB.Net trailed much rarer languages like Lua and Tcl)
Maybe you can't take the numbers at face value because Java is so much older, but I still think the differences are striking.
Make of it what you will, but I think we have to say that the OSS activity is simply much richer in Java than .Net land. I suppose you can argue with me that Microsoft actually does a better job of building tools and frameworks than the Java vendors and OSS just isn't as important to us. I think I'd still say that we don't have as rich an ecosystem of innovation and choice as Java. When you consider that most of our major OSS projects are ports or copies of Java or Ruby tools, we come off even worse than the numbers imply. I guess my real point is that I think we (.Net community) would be better off if we (the developers who do not work in Redmond) were much more actively involved in creating the tools, frameworks, and techniques that we use to do development.