Last year, word swirled in the air that Hewlett-Packard would be the next big PC vendor after Dell to add support for Linux on desktops. So far the official word remains muted, in the realm of "we're exploring options, we'll make an announcement when the time is right", but the guesses now center around HP providing SuSE Linux Enterprise Desktop as its distro of choice. The real question isn't what distribution, though -- it's what kind of support options you'll get, or as they say, which throat to choke when things break.
That's what you're most often paying for when it comes to open source of any kind these days, not just operating systems: you typically get the software gratis, but you pay for some guarantee it will work well. The bigger the distribution or project, the (generally) better the guarantee. That said, I like the fact that the choice exists with major Linux distributions (and bigger open source projects).
So far the choice of distributions for name-brand PCs seems to break down along two lines: SuSE or Red Hat for business and corporate users, and Ubuntu or one of its derivatives (e.g., gOS) for "just plain folks." Dell, for instance, offers all three in various permutations across its product lines -- the first two with its servers and the last with certain Inspiron and XPS machines. Dell's Ubuntu machines can be purchased with varying levels of support for the OS -- as of this writing, one year of "standard" support adds $275 to the cost of the Inspiron 530N. Or you could skip the support and just tough it out on your own with the help of the community -- and there seem to be plenty of people who do that and get along fine.
Contrast this with Shuttle's new low-end KPC systems, which come with a relatively new distro, Foresight -- but Foresight features so many of the things that people are used to from Linux distributions already (the Gnome desktop, the OpenOffice suite, Firefox, etc.) that the fact it's not a "major" distribution isn't likely to be much of a hurdle for the people using it. If we go by whom Shuttle has traditionally marketed to, that's hobbyists and enthusiasts. (The KPC also comes in a kit form, and if you're gutsy enough to buy a kit version of a PC, you probably know what you're doing -- support is something you already do.)
Again, what's nice about all this is the gradation of support possibilities. If I'm setting up an office and don't want to go it alone, I can pay for the help I need. If I'm my own IT, I don't have to pay for something I might never use. My ongoing experiences with the open source edition of Movable Type, for instance: my needs are modest enough that I don't need to pay for professional support. But if it ever gets to that point, I like knowing who I can throttle -- even if I have to shell out for the privilege.