Windows 8 sales are below expectations. I can't say I'm surprised. Of the two main groups of computer users, I see the following:
Casual Users: "They changed everything! Where is the start menu? I'll just keep using Windows 7."
Power Users: "I don't want a user-friendly interface thrown on top of my desktop. I'll just keep using Windows 7."
Eventually, those feelings might change as some of the other advantages of Windows 8 come out (though I've yet to hear many of those, either). But I think it might be at least a year before a significant number of users make that migration.