Hi Dennis, ACR is a little different than PS in this regard. There is still a little difference between viewing an image at "other" zoom levels like 16.7% and 33% compared to 25% and 50%, but not nearly as much as when comparing those respective zoom levels in PS. The sharpening and NR previews when zoomed out should be considered as "in the ballpark" preview estimates and ok when tyring to make small output (e.g., web-sized photos, email-sized images), but if you are trying to optimize capture sharpening and NR for print, I still strongly recommend viewing at 100% to adjust the settings appropriately.
Is the sharpening supposed to be present when I preview the image full screen but less than 100%. I checked, and it doesn appear to be there.
Someone needs to get busy and get OpenGL/OpenCL working in Camera Raw to accelerate resampling.