Windows 8 Developers Preview (~Sep 2011): I installed this first preview on a secondary work machine and I absolutely hated it; I didn’t understand what Microsoft was trying to accomplish and everything seemed far more difficult to accomplish in Metro than it is in the standard Windows desktop.
Note: I got my first android smartphone between these two previews, so I got some experience with phone-style apps.
Windows 8 Consumer Preview (~Feb 2012): I was curious about the direction of Windows 8 since the developers preview so I installed this new consumer preview in a virtual machine. It was much smoother than the first preview and I understood the direction Microsoft was heading. So I went ahead and installed this preview on a new partition on my hard drive and attempted to use it full-time.
I started to view the metro/modern system as a value-added system; I’d still use my desktop for most things but I could jump into a metro app for a break. And oddly enough, what changed my mind about Windows 8 was my experience with apps on an android smartphone and the Pinball FX2 metro app — I had a lot of fun with that app!
One bug drove me crazy, though. I use a slideshow of images for my desktop background and every time the background changed Windows would display a phantom taskbar icon. Over time, the taskbar would be filled with these phantom taskbar entries. That was quite annoying.
Windows 8 Release Preview (~Jun 2012): The release preview was very stable and I was able to use it full-time with no issues. The phantom taskbar problem was fixed and everything else seemed to be working as well as it was in Windows 7.
My only complaint was that Microsoft removed the Pinball FX2 app for some reason; I had to keep a copy of the Consumer Preview in a VM to play that game. But the game was rumored to return when the final version of Windows 8 was released.