Microsoft's Chief Marketing Officer, Tami Reller, has revealed that Microsoft has recently sold over 100 million licenses for Windows 8, up from 60 million licenses sold up to January 2013. Reller also states that the number of devices certified for Windows 8 and Windows RT has grown to 2,400, which is quite a considerable feat.
For Microsoft to have sold 100 million licenses since its launch in late October 2012 means that they are selling roughly 15 million licences per month (Windows 8 has been available for 6 and a half months). Comparing this figure to the same period ending January 2013, which saw on average 20 million licenses sold per month, it seems that Windows 8 license sales are slowing, which can be explained by the traditional dip in sales in the first half of the year.
Reller also states that Microsoft has seen 250 million app downloads from the Windows Store, while "almost 90% of our app catalog" is downloaded every month. Combined with 250 million SkyDrive users, 400 million active Outlook.com accounts and over 700 million active Microsoft accounts, it seems things are going quite well for Microsoft.