The "System Builder" version of Windows 8 Professional is for installation on a new computer (with no operating system installed) or on a computer that is NOT currently running Windows 7, Vista, or XP. This product ("System Builder") is NOT for upgrading; if you are upgrading from a previous version of Windows, then get the upgrade package (which is cheaper).
One great thing about Windows 8 is that it standardizes the user interface across computers, tablets, and other devices. For businesses that combine desktop and laptop computers with handheld tablets and other mobile devices, having such standardization should make folks' jobs easier.
The user-interface of Windows 8 is so different that most ordinary folks will have difficulty mastering it without help. A great many functions of Windows 8 are not at all obvious or intuitive. Unless folks get help of some kind, I forecast storms of great aggravation and anger (perhaps even some violent temper tantrums resulting in equipment damage). Nearly everything you want to do in Windows 8 is hidden until you learn the secrets (even simple things like signing-in or shutting down your computer). Do yourself a favor: get some instruction before you try to use Windows 8, even if that instruction is nothing more than watching videos on a popular video website.
But be of good cheer! One can become pretty good at using Windows 8 very, very quickly. I think most folks, could learn the basics in under 60 minutes with the help of a grandchild (your own or borrowed) who knows the secrets. You could probably become an expert with just four hours of focused, hands-on training led by a professional I.T. trainer. Therefore, I suppose the best way to learn Windows 8 is to work for a large corporation with a wonderful training department and patient I.T. professionals who staff a help desk. If you do not work for such a large corporation, then do yourself a favor and buy a Windows 8 book.
Windows 8 Secrets by Paul Thurrott and Rafael Rivera was very helpful to me. Windows 8 can be extremely frustrating if you do not know the secrets (i.e., there are NO CLUES what to do, because all of the menus are hidden). However, you will NOT be frustrated if you have a person or a book to show you the secrets; after a day or so, your Windows experience will become so automated (like driving a car) you won't even think about it.
If you do not like to read, there are some pretty good Windows 8 instruction videos on a popular video website. Such video training is often better than a book, because you can see the computer response along with a running narrative.
By the way, the "Desktop" is still there. If you hate the new Start Screen (as most folks seem to), you don't have to use it; simply use the Desktop instead (just like you did in previous versions of Windows). After you have setup your Desktop, Toolbars and System Tray (just like you did in previous versions of Windows), your computer will be quick and easy to use. Any of your applications that run under Windows 7 should also run under Windows 8.
While I shall not clutter this review with specific information about Windows 8, I will tell you the most useful Windows 8 "secret" (for me): Memorize and use the "Windows Key" (Winkey) keyboard shortcuts! (The Winkey is the key on the bottom row with a depiction the Microsoft flag; my Winkey is just to the right of the CTRL key.) For example, if you hold down the Winkey and press C, the "Charms" bar will be displayed. The "Charms" bar is perhaps the most important interface in Windows 8. If you learn the Winkey keyboard shortcuts first thing, you will be able to get most things done in Windows 8 right away!
Here are a few of the more helpful Winkey keyboard shortcuts:
Winkey: toggles between Start Menu and last app
Winkey + D: opens Desktop
Winkey + C: opens "Charms" bar
Winkey + E: opens file explorer
Winkey + F: searches for files
Winkey + I: opens the Settings charm (to shut down your computer, for example)
Winkey + Z: opens "app bar" (the menu user interface that is normally hidden when interacting with a Windows 8 app)
Winkey + X: opens the "power user" menu (which includes programs and features, power options, event viewer, system, device manager, disk management, computer management, command prompt, task manager, control panel, file explorer, search, run)
Update (12/13/2012): After several weeks of use, I am really happy that I loaded Windows 8 on my new (home-built) computer instead of Windows 7. Windows 8 is faster and more stable than the Windows 7 that is running on another machine that I use daily. Windows 8 loaded very quickly (20 minutes for a "clean install") and all of the drivers worked without any problems. On my dual-monitor system, I have the Desktop app on the center monitor and the Start Screen on the side monitor. Thanks to two Windows 8 books, I have been learning about "Metro-style" apps and the new world of the Start Screen (look at youtube videos if you don't know what that is). I have been loading apps from the Windows Store and customizing the Start Screen after learning how to add (pin), delete (unpin), resize, move, and group "tiles." I think that most home users (who only need casual web access) will eventually abandon the Desktop entirely in favor of the "Metro-style" apps on the Start Screen. For myself, I prefer the old familiar Desktop for work software. Therefore, I implemented a task through the Task Scheduler to switch directly to the Desktop app on each boot. As I stated in my original review, Windows 8 is very easy with the help of an instruction book; it would have been a royal pain without such a book.
Update (12/25/2012): I also found it helpful to add the following icons to my Windows 8 desktop app: Computer (formerly "My Computer"), Control Panel, and Network. To do this, right click on any clear area of the desktop and select the Personalize option. In the left pane of the Personalize window, click Change desktop icons. Tick the boxes for the icons you want displayed on the desktop (Computer, Control Panel, Recycle Bin, User's Files, Network). Click the Apply button.
Update (5/25/2013): I just finished reading the book Windows 8 Inside Out. While the Windows 8 Secrets book provided great training back when I was completely new to Windows 8 (and just about to load it on my new computer), Windows 8 Inside Out has more information and a better table of contents, thus making it the better choice for my desk reference.