Embrace, Extend, erm, what was the other one ?
While on the one hand, I really can't find it in myself anymore to give a toss about Stallman et als increasingly hysterical jihad against people getting paid for their work, I must say I have always wondered at the fascination of a certain subset of the linux developer community with windows toys. KDE is a straight rip off of Windows 95's interface for instance, all Linux boxes read/write FAT filesystems, samba is a must have and then there's Mono, of course.
I'm mildly surprised that it has taken so long for the beardy wanker to throw his toys out of the pram about it, to be honest. But also mildly surprised that anyone bothered to implement an MS toy on linux. These days it seems that never the twain shall meet. Seems there are still some linux devs out there who are able to judge things without their frothing idealogical zeal getting in the way.
Still and all, while C# is desirable (once you get used to the non deterministic finalisation), ripping off the MS framework is just stupid, if MS really wanted to support platforms other than Windows they would do it themselves. .NET is the single most significant technology to come out of Redmond in years (and yes, that's not saying much), they are literally betting their future on it, development wise, and they really like to get paid.
And to be honest, I, along with most other grown ups, am actually prepared to pay actual money for decent interoperability. Shocking, I know.