Interoperability Summary
Dan'l Lewin recently authored a post at AlwaysOn that I thought was an interesting read - it summarized Microsoft's history of interoperability and cross-platform support, and broke down our existing investments in interoperability into the 4 primary buckets we use to enable interoperability by design: Products, Community, Access, and Standards. You can read more about the overall interoperability mission at http://microsoft.com/interop.
One other thing I picked up here that I found extremely interesting was reference to Sun's Project Tango designed to improve interoperability between Sun's Java Web Services implementation and the Windows Communication Framework. It's great to see this kind of effort to enable interoperability between to heavily used web service stacks.