I wouldn't even go as far as to say that it's Windows 8 that's causing the decline. I am using a Dell Venue 8 Pro now and it's the best tablet experience I've ever had hands down. Better than an iPad or Android tablet.
Windows 8 functions as advertised, the app selection is a moot point, and Windows has gotten Apple beat by a mile in terms of being able to switch into and out of a fully touch or mouse and board UX/UI. Even with dual displays plugged into an 8" tablet I can get a touch UI on one screen and a full desktop experience on the other. The machine runs Photoshop without a hitch while running other light apps. I've coded websites and made GFX in Illustrator. Lightroom, and it's hungry hippo self, runs decently, but don't load up the library.
Then there's games, where Civ 5 does a fantastic job both in the touch and desktop UI.
Now the hardware . . . . . that's another story. I've already had three Dell related hardware glitches with this thing that the normal user wouldn't have been able to recover from.
I don't even think there will be too many Macs.
The way things are going in the high end market, which usually trickles down to the average user, everything is moving to zero client. Where the grunt of the work is handled by servers that just stream pixels to end users. The 48 core 256GB of RAM servers that Dell and HP make are far better at handling any task you can throw at them.
Soon, even the laptop will be a novelty.
Isn't it amazing how history repeats itself? From terminals to terminals.
Personally I really like the concept and idea of Surface Pro. I think the idea is brilliant! One small device that can do touch when you're on the go and when you're at home, you can have it docked to a larger monitor and use it as a desktop OS.
If Windows 8 had been executed much better(I hate side scrolling paradigm personally), it would've sold very well.
Maybe with Windows 9 Microsoft will fix it and by that time Surface Pro should be very powerful as well and hopefully fanless.