Don't be obtuse by equating their use. I don't follow your second line though. Per the last, is there some show stopping bug that is preventing your adoption? Why are you waiting for SP1? Why not force them and then report on your top help desk items?
You, as an IT Pro, are going to say in all honesty that there is zero user weight to adding a completely new UI on top of the familiar that is more than just the Start Menu, both in scope and integration? Now we can quibble over how heavy you think it is, but to say its weightless?
What's stopping us is that we just received Windows 7 certification for our inhouse apps. I'm not about to drop Windows 8 and go through that process again; not until the next computer refresh.
Actually we do have 4 PC's running Windows 8 just to see what kind of traction we got from it and 3 of the 4 users have decided to keep using it. And two of these people are in our design and development department. Their biggest gripe was that they can't access the app store because we locked it down.
And if I base how successful migrations/upgrades are using top help desk items after said migrations and upgrades, I'd probably say they were failures. We prepared for the jump from Office 2003 to Office 2007; training, books the whole ball of wax. We prepared the users for weeks and then we rolled it out. Guess what happened? Influx of "How do I..." tickets. Even though we'd made sure to go through the points we thought would be hard for the users to deal with.
Zero user weight? No; but not as big as most of the people against the change make it out to be. It won't be any different than our Office migration; a whole bunch of "How do I..." tickets until the users learn to navigate the system.