Steve Ballmer's retirement and Microsoft's acquisition of Nokia's phone unit 

Microsoft's acquisition of Nokia's phone unit itself will not make much difference to the fate of Windows Phone. 

Windows Phone is an outstanding mobile OS, much better than Android.  The only significant disadvantage of Windows Phone is its much smaller number of apps. Microsoft is not helping alleviate this. Google does not charge developers an annual fee for publishing their apps, and app updates can be published in minutes.  The latter means a lot to developers. 

Microsoft charges $100 and has a multi-day delay process of approving each app update.  The latter is a significant hindrance to app development.  It seems that Microsoft has never heard of "Continuous Deployment," which many developers embrace, while Google has done its best to promote continuous deployment by allowing instant publishing and automatic app updates on Android.

Ballmer has numerous missteps:

• Windows Mobile (a variant of PocketPC) appeared on smartphones in 2003.  For about 8 years, Microsoft made little innovation on it, and saw later comers of smartphone OS Apple and Google taking over a large chunk of market share.
• Windows ME was a short-lived mediocre Windows upgrade with all kinds of driver issues, the first after Ballmer became the CEO. Many people think it was a disaster. Anyway, customers could completely skip this upgrade and jump to Windows XP from Windows 98 without losing anything.  Ballmer did not seem to learn from it and produced another mediocre Windows upgrade, Windows Vista. Microsoft did not appear to have done any customer survey before releasing Vista. I personally think Vista is better than XP, but one could skip this upgrade to go from XP to Windows 7 without any problem. Ballmer eventually showed his obsession with mediocre Windows upgrades by releasing Windows 8.  Windows 8 is a great OS with excellent performance and decent backward compatibility after some updates, but it has a significant flaw – Metro UI, the default UI.  This is a terrible UI for most tasks of desktop PCs, but a great UI for tablets.  It gives the impression that Microsoft developed a version of Windows for tablets and forced it on desktop users.  Fortunately, it is very easy to switch to the classic UI.
• (to be continued)