A: In the press you will often read:
SharePoint is the fastest selling product in Microsoft history.
Microsoft has been adding 20,000 SharePoint users per day, every day for the last five years.
There are over 65,000 SharePoint customers who have purchased SharePoint (statistics stated at the Microsoft SharePoint Conference in 2011: http://www.microsoft.com/Presspass/exec/kurtd/10-03-11SharePoint.mspx).
Further analysis may question these numbers, but there is no doubt that SharePoint is an extremely large and successful source of revenue for Microsoft, as well as being strategically important, as it helps sustain other Microsoft franchise products such as Office and Windows.