This text is taken from page 56 of the book "Free Expression" by Robbi Joy Eklow, who writes a column for Quilting ARts.
Quote: "don't worry about consistent stitch length. That will come with practice. Yes, judges occasionally comment that my stitch length varies, but I've won ribbons for my free-motion quilting anyway. My feeling is that varied-length stitches are a mark of a human being moving the quilt around, not a machine. Consider a pencil or pen drawing: the line thickness indicates the work was done by hand. Computer drafting programs will give perfectly smooth lines. Art is done by hand. We are doing art here. Strive for small enough stitches that the line will be smooth, but not so small that you can't pick out the stitches with a seam ripper."