I just installed the Windows 8 release preview on a test machine. If you've been around in the past six months and either been on the Internet or watched TV, you probably know that the new UI has done away with the "Start" paradigm. Which is to say, there's no Start orb/button.
Needless to say, the Windows 8 UI takes a little getting used to, especially if you're using it on a computer with a keyboard and mouse. I haven't tried it on a tablet or phone yet, but I can see where it would be much more intuitive to use on a touch device.
Although I'm an early adopter of technology, I'm typically one of those people that immediately looks for the "classic mode" setting. Unfortunately, there's no such option in Windows 8.
If your first reaction to Windows 8 is "OMG, get me a Start button, stat!" there are a number of utilities available - a growing market, no doubt - that will update the UI with a Start orb or menu. Each utility has its pros and cons, so check out this CNET article that has review of three of them.
I was tempted to install one of these utilities. But perhaps I'm rushing to judgment on the UI without giving it a chance. Also, once you get used to using one of the utilties, you miss out on any potential benefits of using the new UI. So I'm going to stick with it and see how it goes. I've still got Win 7 on my primary computer!