Mandriva has this statement on Microsoft's patent game:, and pre-announced
As far as patent protection is concerned, we are not great fans of software patents which we consider as counter productive. We also believe what we see, and until we see hard evidence from, say, SCO or Microsoft, that there are pieces of codes in our software that infringe existing patents, we will assume that any other announcement is just FUD. So we don't believe it is necessary for us to get protection from Microsoft to do our job.
A clear statement, and one that lays down good guidelines for Microsoft: if you want Mandriva to play, you need to provide a compelling reason to do so. Microsoft has not yet done so. Time to put up or shut up.