I have self-backed policy of not mentioning competition if not really necessary, let it be G or M. So as a minimal effort I just quote these carefully selected bits (bias included!) instead of commenting the recent story:
As much as I love Gtk+ and the Gnome desktop, our contributions for our desktop applications and for Gtk+ come mostly from from folks developing on Linux for Linux (with a handful of exceptions). And we are a small fraction of desktop developers.
In my mind what is interesting to me about building applications with Silverlight is that we can create an ecosystem of free software applications that run on all three major platforms: Windows, Linux and MacOS.
I think we can congratulate Trolls that the Qt/Windows, Qt/*nix and Qt/MacOS products and communities are vital and have been for so many years, and also congratulate the KDE community as a whole that the KDE/Windows and KDE/Mac projects are well established.
He is apparently quite excited with capatibilities of .net+silverlight as "Universal GUI toolkit", and advertising it for needs are already covered by long available Free Software offerings like Qt and KDElibs.
The story about "replacements" proposed by Miguel does not end with replacing GUI toolkits or C++/Java with C#, there are his nice words about replacements for the OpenDocument format and Sourceforge/FSF/whatever - all this is syndicated on the Planet G and that is, I feel, exactly what's been criticized by RMS.
Update (Dec 16): aside from the technical concerns (portability), this is more or less how the mono/moonlight business plan appears to _me_: