There is not much reason to switch from Windows 7 to Windows 8, because it makes no difference for desktop apps. However there is no reason not to install Windows 8 on a new machine. You get used to the interface quite fast and if for some reason you don't like the new UI, you can install a 3rd party app to get it back. Getting to the familiar desktop is just one click in the new UI.

Windows 8 is a bit faster, has better auto updating, and has the ability to add the Apps directly from the Store (if you are in to that).