I think this is what will make Windows 8 the least popular OS version in the past 12 years. The interface is so different, most users will feel uncomfortable switching to it. If they want to sell Windows 8 they'll have to evangelize it and its interface to users, just like they need to do it with WP7. Users will not accept it by default just because it's the next Windows, especially with all the inconsistencies between the "Windows 7 mode" and "Windows 8 mode".

I believe most will keep using Windows 7, just like they kept using XP when Vista came. It's actually worse now than it was when Vista came out, because people were already getting tired of XP back then, but still didn't switch. I doubt too many feel tired of Windows 7 already.