You do realise that Steam works perfectly well on Windows 8, right? GfW, or whatever it's called at this particular minute, apparently has a few issues for some (seems to work fine for the majority), but they'll be ironed out sharpish.
Personally I don't know. I tried out the previews on laptops, just testing a few things, and I guess I could happily use it, Metro included... but it doesn't do anything better for me - nothing in it is going to save me time, make things easier or improve what I do, so I currently can't see a single reason for installing it, even at the current price. I might make a backup, install it and give it a proper go for a few days, but I can't see me going ahead and buying a license - unless it's improved massively from the previews, I'll just end up restoring the backup.
I could see the benefit of the change to the ribbon in Office, and now most of the other desktop applications in Windows, and whatever you feel about the change, it is more logical. But I can see a whole world of issues coming up for the technically challenged with Win 8 - it's all swipes and invisible magic pixels (and even then they've been inconsistent in the previews). The majority aren't going to have a clue. Try installing this for someone and not telling them how to do things, such as how to shut down Windows... they're going to go ape @#$%&. It should be brilliant for tablets, but so far the tablets are costing far too much.
I'm much more interested in the effect Windows 8 will have on Windows Phone 8, namely what should be a huge surge in apps. WP8 is starting to look very inviting.