Microsoft clearly is involving Xamarin in this announcement -- parts of Xamarin are going into the same dot net Foundation that's in charge of this, and de Icaza was on stage for part of this. It may be best for Microsoft at this point if they support and involve Xamarin without buying it outright, people who want to use Xamarin with MS tooling can take advantage of Visual Studio integration, people who are wary of Microsoft can use Xamarin Studio and Mono and never officially touch Microsoft's stack while still becoming part of their ecosystem.
