Last Tuesday Microsoft announced the Open Specification Promise, which boils down to a permanent agreement not to sue anyone implementing web services for patent violation. This has been done in consultation with the open source community - to quote Red Hat's deputy general counsel Mark Webbink:
Red Hat believes that the text of the OSP gives sufficient flexibility to implement the listed specifications in software licensed under free and open source licenses. We commend Microsoft’s efforts to reach out to representatives from the open source community and solicit their feedback on this text, and Microsoft's willingness to make modifications in response to our comments.
There's more detail in this CNET article. We also spoke at the php|works conference, attempting to persuade PHP developers that they might at least want to consider running their applications on Windows. One interesting thing mentioned are the efforts to create a PHP to .NET compiler called Phalanger, which should hopefully bring all the inherent benefits of the .NET platform to PHP.
These are interesting examples of how the company is trying to talk to and work with these groups, and improve its image in this area. Okay, so don't expect the NT kernel to go open-source anytime soon - Microsoft still invests a huge amount in R&D and recognises the value of intellectual property. However it's all a good shift away from "open source is bad" to "we think our stuff can do a better job, and here's why"; things definitely appear to be moving the right direction.