The image below shows two shots of the same scene (camera moved a bit so the images aren't exactly identical). Compare the water appearance in the two photos and you will be able to see the difference between shooting with (on the right) and without (on the left) a Vari-ND filter. I have much more to learn about using this filter but wanted to share these images with you and let you know that I'm mostly away from blogging while traveling in the wild west.
This is the West Fork of Rock Creek as seen from under the bridge at the entry to the parking lot for the Silver Run hiking trail. I was balancing my tripod on rocks and myself as well so was having trouble keeping the exact same scene in my viewfinder.