Yeah, I think setting the default file associations to Metro apps is something that really damages people's first experiences with Windows 8 on non-tablets. I find it hard to believe that many people, even "casual" PC users, would prefer this setting, at least with the apps in their current state (which I doubt will change that dramatically by launch). It is easy enough to change (there's even a popup that appears the first time you open a file of some type, asking if you'd rather use a different app) but a standard rule of UI design is that most people don't and defaults do matter.