I wont be upgrading my htpc to Win 8 until I see some serious third party apps in Metro that can take the place of Media Center + MediaBrowser.
My other pcs will be upgraded however. A $40 upgrade to Win 8 Pro is well worth it imo considering the improvements to the desktop that I plan on making use of. The Metro stuff will not get heavy use on my pcs, but I could see myself using some apps if any came out that were compelling. Otherwise, I can just live in the desktop side. If MS could fix just a few issues on the desktop side, it would be a perfect evolution of Win 7. As it is, it gives me good stuff and some not so good stuff.
My htpc works fine now, so I will definitely hold onto Win 7 for a while. Win 8 offers nothing in this area to even consider switching.
I'm really not sure what Win 8 will bring success wise. If you just went by some power users posting around forums like this, you would have to say its going to be a disaster. But I think the reality is one big gray area.
I think this release will expose the huge gap between the power user and the average user, exposing the big differences in what one group likes and what the other likes. I think for power users, the issue here is that the consumer seems to be getting more focus then they should. Windows is traditionally a power user (or business user) first, consumer second software. This time MS feels they had to do something that was targeting the average user in a big way. That became Metro and here we are. I doubt we will see much business adoption, but lets be real here, even if Win 8 was held up as great by everyone, most businesses don't upgrade to the latest and greatest for some time. MS knows this as well and they probably are perfectly happy to keep getting companies upgraded to Win 7.
So MS' big gamble is that the design is a hit with consumers on tablets and that app devs seriously support it. Apps will help even desktop usage if they are compelling enough. I just hope they really try to address the issues on the desktop side while working to make the Metro side more robust. It could turn out that Win 8 gets average consumers excited, while its not until Win 9 that power users see their issues resolved. Of course, MS may treat this OS differently then past ones and release significant OS upgrades every year more like a mobile OS release.