OK. We're getting serious here.
If you've read this blog, you know that I use Linux, a free (in both senses--in Spanish I'd call it gratis y libre) operating system that runs on a wide variety of hardware, notably including commodity x86-based computers. There are a number of organizations, most notably the HeliOS Project, who take advantage of this by refurbishing used computers, installing Linux on them, and giving them to people (in the case of HeliOS, central Texas children) who could not otherwise afford computers.
Well, Microsoft has come up with something that will eventually make that impossible.
If you look around at off-the-shelf computers and peripherals, you'll notice that typically either (1) they're made by Apple or (2) they have a little Microsoft stamp of approval saying something like "Designed for Windows [insert version here]". Microsoft is now working on the successor to Windows 7, Windows 8. Windows 8 uses UEFI (son of BIOS). By itself, that's no big deal, save perhaps to anyone wanting to upgrade to Windows 8 without having to buy a new motherboard that has UEFI; Linux has been able to work with it for over a decade now...
A few days ago, Microsoft announced that to get the Microsoft stamp of approval for Windows 8, computer makers will have to have the UEFI "secure boot" feature enabled. With this, the computer will only boot programs that have a digital "signature" it knows about. This has the potential to preclude installing anything but Windows 8 on such a computer, because the easy way out will be for the computer maker to only put in the signature for Windows 8. (There are also hardware driver issues as well, since those have to be signed to work in that secure mode.)
Will it be possible to turn that mode off? Perhaps, but OTOH, any computer that offers that possibility may well be branded as insecure (perhaps you recall Microsoft's campaign against selling "naked PCs", i.e. computers without an OS (*cough*Windows*cough*) already installed on them... this would be much the same).
So the time may come when the only off-the-shelf computers you can install Linux on are ones so old that nobody would have them. You can get any OS you want... as long as it's Windows.