More likely candidates for built-in touch are mobile PCs, including traditional clamshell laptops and convertible units that you can transform into tablets, either by concealing the keyboard or by detaching the display, which can act independently as a tablet.
Windows 8 is a different experience with a touch-enabled display, even if you're using such a display with a stock desktop system. At first, you don't think you'll use the touch capabilities. But then your kids come up and start touching the screen--after all, these days young users are growing up expecting displays to be touch-enabled. I've been running Windows 8 on a desktop PC equipped with an Acer T232HL touchscreen display, and although I use the mouse some of the time, I find myself reaching out to use gestures on the screen at other times.
As for other desktop-PC options, look to the emerging generation of all-in-one PCs, such as Sony's 20-inch Tap 20 and the updated version of Lenovo's A720, which are shipping with Windows 8. The Tap 20 is unusual in that it has a built-in battery, which allows you to move it around the home easily and use it as an oversize tablet.
With any touch display, you tap app tiles to launch software, swipe the display to access other features, and use multitouch gestures, such as pinch-to-zoom to enlarge or shrink what's on the screen. Touch support makes the Start screen more usable, though the user interface still has some rough spots. For example, if you swipe your finger in from the left just a little, you get thumbnails of currently running or suspended applications. But slide it a bit too far, and one of those apps takes over the screen. You need to develop a delicate touch (no pun intended) to take full advantage of the interface.
Despite Windows 8's new features, performance tweaks, and improvements over Windows 7, its touch support will likely be the defining factor. And despite some imperfections, the touch interface works smoothly. After you use it for a few days, the old way of using Windows will start to seem slightly cumbersome.
Windows 8 on tablets