Having been using win8 for around a year now (MS employee), I really haven't noticed it getting in the way. I rarely find myself using a mix of both - either I'm in metro mode or I'm in a desktop mode. If I'm on a desktop, the keyboard shortcuts (win + type anything has gotten a lot better since windows 7) work wonders. They've made a lot of speed improvements that have been really nice. If I'm in metro mode (which admittedly I rarely am, it's just not that useful right now on a desktop), I tend to stay within that modality. I think that right now Microsoft is preparing for future hardware with this release. On traditional desktops, this doesn't make sense. But on things like the new surface I can actually see it working well.
I have also used products at the companies I've worked for that 1) worked well for me and that 2) nobody else can figure out. Eating your own dog food is a good first start, but never believe it is sufficient to really understand how users will use a product.
I've had to configure my helper applications to avoid getting thrown into Metro from Desktop by accident; e.g., setting my PNG viewer to Chrome instead of picture viewer. I haven't found much to in Metro yet beyond browsing my applications, but I think the whole concept is very cool. Even on my Samsung tablet I find myself in desktop all the time...b/c OneNote is just that good.
