Microsoft went and did an interesting thing - they released some of the .Net framework source code. From a development point of view, this allows you to step through the code when debugging, which is tremendously useful in troubleshooting bugs. It also helps you build new things on top of it, because you understand what it does or doesn't do better.
The code is available under via a "Microsoft Reference License". This says that while you can see the code, you can't copy it, or modify it for distribution. This is really a huge shift in philosophy for MS, who have previously gone out of their way to protect code from being publicly available.
This is an interesting response to perhaps one of the biggest advantages with open source products, and one that I'm paying a lot of attention to given that we are in a similar position with our proprietary, closed source, product. I'm sure our customers would welcome the ability to see the code when building out customizations on our platform.
This also highlights that the real value of a product, particularly framework and platform based, is not the code itself but how it helps your customers achieve their goals. The fact that I as a developer now have access to the source code makes the platform more valuable because I can spend less time learning it and dealing with bugs (be they mine or in the platform). Put another way, providing access to source code does not diminish IP value, but does serve to increase the value proposition of the platform.