Whipped Backstitch is one of my favorite stitches. It’s easy to do and it makes smooth rounded shapes. Not many stitches in needlepoint can do that. You can use it to outline round shapes (like the bubbles in Wicked, above).
But where it really shines is to make letters. I used it for the letters in Happy Spring, above. Mary Corbet is doing a series on lettering right now and has a detailed tutorial on whipped backstitch on her blog, Needle n’Thread.
Remember when using this tutorial that Mary is doing embroidery on fabric, not on canvas. To adapt this stitch to needlepoint, make sure your Backstitches go over at least two threads as much as possible. This makes a very blocky line, usually not pretty at all, but trust me, everything smooths out once you whip the stitches.