The biggest risk that Windows 8 brings is that it's not just a no brainer upgrade. It requires training, it requires consideration of the costs and benefits. And once you are on that road then you are on a road that could easily lead you to non-windows alternatives. iOS or android tablets, linux workstations, etc.

And all of this because MS was too cocky and decided to go all in on metro instead of trying for a smoother, more gradual transition.