@Stephen - you assume the deal happened spontaneously, but it might very well been cooking for some time. Such dramatic strategic shifts take preparation. Microsoft has been worrying about competitors significantly lesser than Qt, as a good crossplatform library Qt is a viable longterm thread for MS. People use Windows because their programs can only run in Windows, Qt makes it easy to write programs that run on other operating systems, including Linux, which is free. And I myself wouldn't ever bother with Windows if all my programs were available for Linux. Besides being cross platform, as a native C++ framework, Qt has a performance and memory advantage to .NET too.
There is plenty of room in the mobile market, in fact if Qt steps in, it will be WITHOUT competition, as there currently AREN'T ANY native cross platform frameworks. With the Android SDK your application only runs only on Android, with the iOS SDK your applications runs only on iOS, same for Microsoft's development toolchain, even with SDKs like MoSync or Marmalade which support most mobile platforms, you don't get desktops.
There is definitely a place for a ALL IN ONE solution, being capable of running on all major mobile and desktop platforms, and many developers would be interested into making their applications available everywhere in an effortless way. We have many brands of cars too, it doesn't mean there is no room for a new, versatile vehicle that runs more efficiently, on all types of fuel and across all terrain, figuratively speaking.
Qt gaining mobile market share is only illusional for as long as it is in the hands of Nokia, who will not dedicate to supporting major mobile platforms, and has no popular platform but uses that of MS which Qt doesn't support. But in the hands of another company, Qt has the potential of rising in popularity very quickly. Android alone is about 50% of the mobile device market, and having dealt with the Android SDK I'd chose Qt over it any day, and I see no reason why this won't apply to most developers. Android is on its way to desktops too and will pretty soon start stealing market share from Microsoft. Just look at how much market share Chrome managed to steal in just a few years.