Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
Excluding complete vaporware, like the intriguing possibility of Google delivering the Next Big Thing in operating systems, I think Apple is the most perfectly poised to strike a killer blow. But it will have to untie the Mac from OS X. Some people want attractive, killer-design, expensive hardware, and that's why they buy Sony and Apple. Other people--and a heck of a lot more of them--want function-over-form, inexpensive hardware that they can buy, sell, hack, and tweak like any other commodity. They buy Dell, Gateway, and Windows. If those people start buying Tiger, Apple suddenly owns the joint.
This scenario is not even remotely out of the realm of possibility. Tiger is based on Unix, for Pete's sake. There's no reason it can't run on Intel-based PCs. Apple's already using Intel processors in its Xserve RAID storage system. Steve Jobs said in 2003 that it was technically feasible to port OS X--then in Panther stages--to any processor, but as recently as February, Apple chief financial officer Peter Oppenheimer said the company has no plans to switch platforms. It should. People would use OS X if they didn't have to buy a new computer to get it (heck, by some accounts, Tiger and Longhorn are darn near the same thing). Apple should do the switching for them.
Linux will almost certainly beat Microsoft in the server space, given time, but what about the desktop? The most promising contenders have either faltered or failed to catch on. I truly believed Red Hat could succeed on the desktop, but, along with a series of other mistakes, it launched this bizarre, confusing Fedora project, trading away brand recognition and confusing consumers about whether it would even support the new desktop product. SuSE Linux was bought by Novell and has since focused mainly on its Professional packages. Xandros sold supercheap operating systems, even giving away a stripped-down desktop product, packaged it with familiar compatible apps such as OpenOffice, and simplified installation. But it just never caught on. Linspire, formerly Lindows, was really just a vehicle for low-cost PCs and operated more like a Web service than an OS.
I'm not convinced that the Linux community can pull it together enough to get behind one truly dominant distro. Part of the problem is that the anarchic and altruistic nature of the open-source movement keeps it from sacrificing features and quality in order to carpet-bomb the market with a product that works just well enough for mass adoption. That's the Microsoft MO, after all. And even if Linux can pull it off, time is ticking. Microsoft will pull it together eventually, and Linux's moment may pass. Still, I'm willing to consider the possibility. Linux, your deadline is Christmas, 2006. Let's see what you can do.