Yes I do it, with a ruler and fine thread (MicroQuilter from Superior is my new favorite choice for this chore). It is harder to do, because obviously you're supposed to stay in the ditch, and not all ditches are as straight as they should be. In fact a ditch is not really a ditch if the seam allowances are turned one way and then another within the same seam, and even when they're pressed the same way they sometimes flip around on their own when the top is put on the longarm. I don't dislike doing it, but I'm not overly concerned if my very fine thread strays from the ditch (and it always does, here and there.) I do it either to stabilize the quilt before doing more extensive quilting, or to highlight design elements in the quilt. I don't charge extra, because I only quilt for myself and a few friends.