August 1, 2016 Edited to add: In the years following this post which started it all, I have created two classes with Craftsy on this technique. This special instructor's affiliate link will take you to them and allow you to purchase them at a 50% discount all the time. No need to wait for a Craftsy sale! There are multiple sources for ruler feet and ruler for use with this technique as well,and I now have an online shop where I sell a well-tested selection of rulers and supplies I use.
In my post on my butterfly wall hanging, I mentioned that I had done free motion curved cross-hatching using a long arm ruler. I had heard that some folks were trying this on the bigger sit down machines like APQS George (Love!) or the HQ Sweet 16. But I had not actually found anyone who was doing it. After purchasing Karen McTavish's book, Custom Curves and the accompanying DVD, I was disappointed to see that the demonstration of crosshatching on a domestic machine was done with a walking foot. (Love this woman's work and her books!) I thought at least it could be done by following the marked lines free motion.
Quilter's Rule was at the show too, I picked up a double S curve ruler by Rhonda Beyer, Karen's partner in the Custom Curves book.
The two essential things for ruler work on your sewing machine after the ruler toe is to have a good smooth surface to glide your quilt over as you stitch and to have a "grippy" ruler. I used my cheap ruler grip method-- clear nail polish and a sprinkle of salt. It worked like a charm!
Since the ruler foot is a 1/4" foot; meaning the distance from the needle to the outside edge of the foot, place the ruler 1/4" away from where you want the line to be stitched. Then I rested my left hand on the ruler with my pinky and ring fingers off the far side of the ruler (onto the quilt) and slide the quilt and ruler along the side of the foot as a single unit. At first I tended to press too hard down on the ruler and quilt, making it difficult to move, but I soon got the hang of it.
This method can be done with a regular darning or free motion quilting foot and/or rotary cutting rulers, but you run the risk of sliding the ruler up under the needle. This would break your needle and possibly mess up the timing of your machine.
I found the method to be easier than I thought it would be, and since I did this ruler work in the corners of my quilt, I found that the ruler helped control the edges as I stitched, keeping them from bunching up as I stitched back in toward the quilt. I found it to give much better results than following a marked line.
Give it a try and let me know how it turns out for you!