Here's my .02.
I love it. I am able to get everything I need from all of the tabs (I only do part modeling and assembly), rearranged where I want it in one part modeling interface. I find it extremely flexible. Everything I use the most often is in the middle of the ribbon, and the most used commands are at the bottom near the graphics region. I've even go so far as to modify the Import Data Doctor ribbon to include the measure and appearance tabs so I'm not flipping between tabs to get at those items. Adding our own custom commands is easy as well.
Where it can use some work: The Part Modeling ribbon is NOT the same as the "Activated Part in and Assmebly" ribbon. This is annoying. I had to make the modifications twice.
However, since I've made these changes, I'm far happier with this interface than with the old Wildfire or 2000i interface. I have exactly what I need at my fingertips.
The only other thing that annoys me is (as an administrator) that everyone has their own system, and when I'm helping someone I tend to look for my layout instead, but that's the same as if I try to use one of my mapkeys that the user doesn't have. I can say that everyone here is pretty happy with it, even if it had a slight learning curve.
What they can fix, though I wouldn't put this as a priority, is the annoying "To select an object, hold down the ALT key message" so that when I click the box, it never never never shows up again.