Macintosh OS 9
The Mac operating system has changed over the years but not in very dramatic ways. In fact, anyone who has used OS 9 will know exactly how to use OS X. If you have used Tiger (10.4) then you can use Mountain Lion (10.8) without much todo or fanfare.
Steve Jobs knew that tablets were the future of computing and built the entire Mac eco-system around that idea. The features you find in iOS are readily becoming available in Mac OS X. This is deliberate.
What Microsoft is doing with Windows 8 is try to bridge a gap that has been building over a period of years. They are trying to jump ahead to a point that they were not preparing for. While Windows dabbled in touch screen interfaces, they saw something that was really “cool” but didn't really know how to apply it and use it to their advantage. I remember seeing Vista for the first time and listening to Microsoft tell me how awesome it was and was going to become. I also remember yawning and noting that all of those “cool new features” had been in Mac OS X for months or even years.
I am willing to bet (without having read the entire Steve Jobs biography) that Steve saw an episode of Star Trek The Next Generation's use of the PADD and snapped his fingers. I don't doubt that for a second because after watching the show, I myself wanted such a device. Man, the things you could do with a tablet computer! Steve Jobs did the same thing with the Xerox interface. While Xerox may not have fully understood what they had, Steve Jobs did. That is vision.
That is what Microsoft doesn't have.
This version of Windows is such a big jump from Windows 7 and so confusing to such a large base of users that this whole thing simply “smells” bad. Big jumps in OS are usually bad for consumers. I haven't even mentioned IT folks that may end up abandoning Windows in the workplace all together. They will have to weigh training hours, troubleshooting time, and costs against other alternatives that are much cheaper and offer less of a shock to their users. Let's face it. Windows in the workplace is expensive.
Windows 8 is such a big jump that it would be like paying someone to shoot you in the face if you are an IT guy.