I suspect Microsoft will end up surprising us - pleasantly. They're not buying Nokia to integrate it into some existing division where it'll get lost and subsumed.
Just look at how it's handled recent large acquisitions before Nokia, such as Skype and Yammer. They're left alone to do their own thing, with pretty much zero meddling, and a gradual and non-disruptive integration into the MSFT ecosystem.
In the past year almost the entire Microsoft management has been replaced, and it'll be very interesting to see how this plays out.
Nokia has been very strong in design, and Windows Phone is very clean and design-focused (fonting, layout, themes, etc), which was part of its appeal to Nokia.
Unlike the past, there's a new openness that isn't fixated on Windows to the exclusion of everything else. Lots of recent examples are evidence of a massive mindset shift inside Microsoft ... Office for iPad before WinRT, apps for Android and iOS, shifting large chunks of dot Net into open source, etc.
The biggest challenge Microsoft faces, I suspect, is that most of the market still thinks it's the old Microsoft, whereas it has humbled and moved very significantly.
Watching the mobile space very carefully because I'm now fully invested in WP and like everyone else I want decent hardware.