I did use the 10.EX's as my "everyday" ski last year and they worked great. They replaced a pair of X-Scream Series.
When buying the skis last fall, I looked at the 11.20's, etc. I just felt that the typical midfat ski (granted that definition is continuing to evolve) was more of a compromise than I wanted. I don't think that a perfect ski exists for all conditions and I don't ski all conditions in equal doses.
The 10.EX is much better for powder, crud, cut-up powder, wind-blown crust, etc. (i.e. basically everything you find off-piste) which is what I ski mostly. Yet, it still carves great (but big!) on the empty, early-morning, fresh groomers when I want to race Hermann in my head.
It is not a pure deep-powder floater; but I don't see enough of those days to warrant buying a fatter ski. It also sucks on hard bumps but so do I (and so do most mid-fats). It is a handful when trying to shorten the turning radius on hard, crowded groomers; however, I tend to avoid those conditions anyway by heading back to the bowls.
After reading all of the reviews last fall, I picked the 10.EX as it seemed to best match up with my typical skiing. However, if my skiing was more concentrated on the groomers or the bumps, I would have selected something else.