Windows is pretty much competing with itself at this point, and Win8 isn't offering compelling reasons to upgrade. Metro is a compelling reason not to upgrade. Windows Phone is doomed to be an also-ran, no matter what MS does.
Tablets are a fad in the consumer space which will fizzle out in 2 years. Microsoft won't be able to break into this market, just like their other consumer-oriented efforts (Zune, Kin, Windows Phone... everything except XBox) failed. However E-readers will continue to sell. Tablet equals fancy electronic clipboard... if you don't havea sue for a clipboard, you have little use for a tablet. In certain vertical business markets, tablets can make sense. In the end, tablets are for consumtion, not production, and touch UIs are a step backward. The PC isn't going to die any time soon.
I suspect the OEMs are already looking for ways to hedge on Windows. They'll push back harder when their windows distribution agreements come up for renewal, because Win8 is a failure and MS is encroaching on their turf with the Surface. The big OEMs will start seeking partnerships with major Linux distros soon, preparing to launch hardware with Tux stickers in 2015 or 2016. And all of them will be begging Valve to let them pre-install Steam. Pressure from the OEMs will force AMD, nVidia, and Intel to get their Linux video drivers up to snuff.
The units will be slightly more expensive because the OEMs won't have libraries of crapware at the ready, but most people on /. will agree that's totally worth it. Even now there's little reason for the average person not to drop Windows for a real OS, and by the time all this happens, it'll be even easier.