You might surprise with the title, but it's true. Microsoft is going to work closer with Open Source community. Their first step was submitting its shared-source licenses to the OSI for approval. So far, Microsoft has released nearly 650 projects using their shared-source licenses. They even make a new site on their primary site to give brief detail about their efforts to work with Open Source community.
But, even though they are going to work closer with Open Source community, doesn't mean that they will release their mainline products' source code for public domain, as they have became the main asset of Microsoft and it will remain the same. So, don't expect Office (or any version of Microsoft main product) to be released using GPL or any other common Open Source licenses.
What surprised me is that in the last few years, some of Microsoft executives said that Open Source is not reliable and they don't deserve to look for, but now, they have worked together with Open Source people.
What i'm hoping from this move is that Microsoft will work better with formal specifications, mostly that has been defined by international organization. For example HTML/CSS Specifications. In the past, Microsoft tend to create their own implementation. As the result, many web developers has to "hack" their code in order to have working code for multiple browsers, just to support old version of IE. They are working better on this, but it should be improved in the future and we all are hoping for that with this move.