We're going to see some big changes in the way we use computers in the next few years. Most consumers, when not at work, just aren't going to need full desktop workstations like we do now. I'm including Mac, Windows, and Linux here, desktop, mouse driven workstations. The vast majority of stuff we do while not working, at home, is consuming content with occasional writing, tweeting, email etc. Yes, there are always going to be people at home who want to produce more, either writing, programming, video, whatever, but not most.
Replacing the desktop for consumption will be touch based mobile devices. Phones and tablets. Mouse based operating systems just don't work well in this environment. Operating systems designed from the ground up for this purpose are going to drive this. We've seen the iPhone prove this, and iPad is pushing it further. Android can compete, and in the next couple of years we'll see others try, including Microsoft's Phone 7 OS, and the competition will really make mobile computing explode. I suspect the heyday of laptops and netbooks is gone too.
Content producers, workers, are going to be using desktop workstations for a while yet. You just need a bigger surface, better multitasking and more input richness than a mobile device can provide. Personally, I think Windows 7 is really good in this space, but that's a religious war for another day.
Still, this is bad news for Microsoft and Intel, unless they can move in this direction faster. Microsoft may be able to follow Apple with Phone 7, but they are three years behind at least, with another six months until anything happens. Intel just don't have anything decent for mobiles, ARM has it all over them.
It's going to be all Apple and Google in a few short years. Let's see what HP can do with Palm and WebOS.
[Update - some iPad experience showing exactly this]
[Update - TechCrunch calling it the Third Wave, this site agrees with the threat to Windows]