Based of its own sources, website Neowin believes that the install base for Windows 10 is already passed 25 million and "may be as high as 27 million." The adoption rate isn't as ferocious as it was earlier at 1500 installs per second, but that's nothing to scoff at either. Microsoft has yet to confirm these staggering figures.
I have yet to be one of those followers though, what with multiple bug reports with automatic updates, Solitaire being behind a paywall (not that I really care about Solitaire but just the principle behind DLC), and spotty video game support. A patch is scheduled to release later this month to even out some of the kinks.
However, the benefits of the new OS (DirectX 12 is tasty) have apparently convinced many to convert, especially since those with an activated version of Windows 7 or 8 can get Windows 10 for free. Which is sort of the point for Microsoft, who wants to make sure that adoption rates are high for the success of future applications.
Have you upgraded to Windows 10 yet?