For about a year now, I have been playing with Windows 8 in its various forms. The long and the short of it is that to take advantage of the new features of Windows 8, you need new hardware. If you have an existing PC, you certainly can use Windows 8, however you may find it cumbersome and much of the interface and new style metro apps may not make a lot of sense.
I have three PCs in my home. The first is an aging desktop PC, which today is little more than my media streaming and download PC. It probably doesn't have a lot of years left in it and while I have Windows 7 running reasonably well on it, I can't imagine it running well with 8.
The second PC in my home is the main PC I use for work. It's a 15 inch Sony VAIO laptop that could certainly support Windows 8 from a specification perspective; however I feel that the additional features don't offer any value to me. The work I do is primarily with software that would run equally well with Windows 7 as it would with Windows 8 so I don't see why I should part with the $40, no matter how much of a good deal that is.
The third PC in my home is an Acer netbook that is about a year old. It's primarily used by my wife and is the one machine that I seriously thought about upgrading. Since it’s a netbook, it came with Windows 7 Starter Edition. Windows 7 Starter Edition is a pretty basic version of Windows and the upgrade would provide additional functionality. That said, the resolution of the netbook will mean that it doesn't natively support the metro environment so again, I’m not sure it’s a good choice here as well.
So I've read the reviews and played with the previews and I have come to the conclusion that Windows 8 is not a great upgrade path for those with existing hardware. You next PC or PC-like device will come with Windows 8 installed, however I just don't see the value for me right now.