Estimates are that there are over 690 million Windows 7 installations. 
If they convert to Windows 8 at one per second, day and night, 7 days a week, 365 days a year, it will take over 20 years. Better hurry up.
690 Million potential Windows Store customers.
690 Million.
About Jesse Liberty
Jesse Liberty has three decades of experience writing and delivering software projects and is the author of 2 dozen books and a couple dozen online courses.
His latest book, Building APIs with .NET will be released early in 2025.
Liberty is a Senior SW Engineer for CNH and he was a Senior Technical Evangelist for Microsoft, a Distinguished Software Engineer for AT&T, a VP for Information Services for Citibank and a Software Architect for PBS. He is a Microsoft MVP.
I’m normally an early adopter but Windows 8 has not made it onto any of my machines. The closest it have got is a VM. Like me, every other develop I know has tried it and then removed it immediately as they have found it unusable.
I think it will be popular on tablets and the like. I cannot see it gaining much traction in the world where classic desktop interfaces are needed – i.e. the corporate market.
@bill I disagree. We have been using Windows 8 in beta with a handful of games and apps on it. If Windows 8 can deliver on quality apps pretty soon people with Windows 7 will look at us with 8 and say, “How can I do that.” I think that is what Jesse is getting at.
The more developers who jump on board the more consumers will look at Window 8 with envy. There is only 690 million potential customers who will come if we can create a space that invites them. We are the ones who need to trail blaze and get some quality apps out there. Then they wont have to be dragged in to update, they will want it.
I doubt that all Windows 7 users will convert to Windows 8. I know that I am recommending that casual users (like my wife and some neighbors) stick with Windows 7. The reason is the silly “Start” screen in Windows 8 gives them nothing of value and a lot of confusion.
I have gone to Windows 8 and most developers will follow suit. I think Windows 8 is a better OS but just too confusing for the those who just use their machine for simple stuff like email, web browsing, and a few Office apps.