I don't expect to hear very much in the way of Windows 10 success until at least in to 2016.
I'm sure that Microsoft will soon be trumpeting success on the basis of large numbers of home user installs. And for the majority of home users, there's three simple things that make this inevitable:
1) Most/all users don't read and understand the EULA
2) Most are ill equipped to understand the privacy issues that are the major concern
3) "free" trumps all other considerations
On that basis I'd guess that Microsoft will see very rapid uptake of W10. Business will remain loyal to W7, and we can expect all flavours of W8 to be end-of-lifed as soon as indecently possible, in the hope of forcing the holdouts to roll over to W10.
Not a very pleasant scenario, but one that seem inevitable with most national legislatures "bought", and most privacy regulators utterly ineffectual.