It is a risk, but without risk MS would rot. People hated Vista but loved 7. Part of that was some polish missing from some new approaches in Vista, part of it was issues that were resolved with service packs. I think most of it is that MS tried new things with Vista, and people complained because they don't like change. Then people tried 7, and much of what they loved with 7 were things that were actually introduced with Vista, but polished a bit in 7. I think we'll see the same thing with 8 - people will (and are) freak out because of change, but by the time the next version rolls around, the shock will be over, and MS will know how to apply some polish to things to smooth and sooth the experience. It's not that 8 is or will be bad, it's that people take time to adjust to change, and the next version will polish new things tried in 8.
That said, one thing that seems to be a big differentiation between Vista and 8 is that Vista's new features seemed to bring some software bloat with them, while 8 seems to be keeping that to a minimum, or even reducing bloat, and at the same time enhancing efficiency with some new tech, which makes it that much more efficient.
I'll be installing 8, but keeping 7 in a partition as a security blanket. But frankly, I doubt I'll use 7 much as long as I don't find any program or driver issues.