I too have learned a lot of proper detailing from Greg and some of the other senior posters (CM5GO, TCM, Atomic80 among others).
One of the tips I picked up was to use the CD method for determining what scratches and what does not. Take a new CD (preferably one you don't care about

) and rub your favorite towel/rag/sponge/mit across the shiny back. Keep to one direction. Now examine under a good light, maneuvering the CD so you can really see the surface.
Are there swirls or scratches? I discovered right away that the cotton towels I was using were scratching like mad. I moved on up to microfiber towels, and was lucky that the first brand I picked did not scratch. However, I was still getting swirled. More CD experimenting, and I found that the stitching used on the outside edges of the MF towels was also scratching! I cut all the edge seams off.
Still introducing swirls, albeit at a much lesser rate, I tried the last item that was still touching my paint: the sheepskin mit. I tried it dry against the CD, and completely swirled it. I knew it couldn't be that bad since my car was not that bad, so I tried it with soap and water just the way I wash it. This did not scratch the CD. I now keep the mit soaking wet and very soapy while cleaning.
Understanding and identifying your swirl sources will provide the most swirl reduction for the least amount of effort. As Greg has said before, you cannot keep it swirl free, you can only control the rate at which swirls are introduced.
Mike