In Real World Adobe Photoshop CS4 for Photographers,, Chapter 10, "Sharpness, Detail, and Noise Reduction," discusses the three stages of the sharpening workflow advanced by Bruce Fraser: capture sharpening, creative sharpening, and output sharpening. (You can read more about that sharpening workflow in his bookReal World Image Sharpening with Adobe Photoshop CS2.) Older versions of Camera Raw supported only the first two stages; the Sharpening tab handled capture sharpening, and the Adjustment Brush let you apply creative sharpening. Camera Raw 5.2 adds support for output sharpening, using new settings in the Workflow Options dialog.
Output sharpening specifically means that the new sharpening options apply to an image only when you generate final images from Camera Raw. You don't actually see any difference in the Camera Raw window, because you can't accurately use it to preview sharpening on another medium such as paper.
Because output sharpening is intended as a final sharpening step and calculated assuming that you've already set the image's final size and resolution, you shouldn't apply output sharpening at all if you plan to resample, resize, or composite the image further after it leaves Camera Raw. Output sharpening is primarily a convenience for those times when you don't need to make any further corrections after Camera Raw—and those instances are becoming much more common as Adobe has continued to add powerful nondestructive editing features to Camera Raw.