http://www.theregister.co.uk/2008/02/21/microsoft_goes_open/

http://www.bizjournals.com/losangeles/prnewswire/press_releases/national/Washington/2008/02/21/AQTH065

http://www.microsoft.com/presspass/presskits/interoperability/default.mspx

http://msdn2.microsoft.com/en-us/library/cc216517.aspx

http://msdn2.microsoft.com/en-us/library/cc216514.aspx

http://msdn2.microsoft.com/en-us/library/cc216513.aspx

http://msdn2.microsoft.com/en-us/library/cc197979.aspx

I don't think I can explain the benefits these actions could have as they're so wide and varied.  I'm not mistaking them for pure altruism, however for a Microsoft platform developer, I'm incredibly excited by today's news of opening up API's and providing comprehensive internal documentation.  I had a quick flick through some of the documentation available already, on the day of announcement, and it seems to be of high quality and revolving around key windows properties.

Happy times!