Bill Gates has released an Email on the importance of Interoperability.  One of things that Bill does well in his Email is highlight two distinct areas for Microsoft technologies and interoperability, which I firmly believe in:

1.  We work with what you have - regardless of whether it's a mainframe, midrange, message queue, Java, COBOL, RPG etc.

2.  We are designing for interoperability - looking at the investments we have made in XML, Web Services and the standardization processes, applications that you write today really are designed to be interoperable with other platforms.

You can read the full executive email here.