According to NetMarketShare, Windows 10 now makes up around 7.94% of all desktop PCs. For comparison, all versions of Mac OSX combined total about 8% on this survey. It is behind Windows 8.1 and Windows XP though, which sit at 10.68% and 11.68% respectively. Windows 7 is still the overwhelming majority at 55.71%.
The OS has a few controversies associated with it, though. Some are warranted, some are not, and still others lay between. The first issue is that the reservation application has been known to download Windows 10, even without permission to do so (and redownload the several-gigabyte file if removed). This isn't counted on the market share survey of course, since the OS isn't actually installed, but it can be annoying for users will small main drives or metered internet connections. For people with satellite broadband, this will probably ruin your whole month.
Microsoft has also just announced that Windows 10 will be pushed to Windows Update for Windows 7 and Windows 8.x at some point in 2016. It will not automatically install, you will need to accept the EULA, but it will automatically download. Intentionally.
There's also some (many) concerns about privacy and data collection policies. Part of it is because Microsoft is pushing a free operating system without a clear business model, which leaves a lot of room to speculate what the value actually is. Many of these concerns aren't really possible, if only because too many people would need to be involved for the lack of leaks, but some level of concern is useful. For instance, there has yet to be a sufficient explanation of what “AutoLogger-Diagtrack-Listener.etl” does, precisely and specifically. Does it pipe everything you do to every advertiser and government acronym in the world?
No. Of course not.
It is an area that Microsoft, and basically all of their competitors, should improve upon, though.