As promised, here's a tutorial on duplicate stitch! Before I even got pregnant, I knit a quick little baby sweater and duplicate-stitched the word "baby" on the front. I didn't know whether he would be a boy, or a girl, but I felt pretty certain he would be a baby -- and I thought it would be pretty funny for a baby's sweater to state the completely obvious. (Which reminds me, it's Measure's 3-month birthday today! Maybe I should bake a cake.)
Duplicate stitch is useful for when you want to add a little something to your knitting, but both stranded knitting and intarsia would be fiddly. Also, while you definitely want to plan stranded patterns and intarsia ahead of time, you can add duplicate stitching long after you've knitted the garment.
Click on the chart for a larger image, and feel free to use it if it works for you. Writing your own charts is pretty easy, though -- your knitting is done, so you can just sit down and check out the amount of stitches and rows you want to work over, and chart accordingly. I knit the swatch for this tutorial in an aran-weight cotton blend (in Project Spectrum colors, naturally), and knit it a little loose so the stitches would be clear, but really I think this works best when your knitting is tight -- it helps the duplicate stitch to "pop" and cover the stitch underneath.
To begin working, cut a length of contrast yarn and thread it through a tapestry needle. No need to knot, just be sure to leave a tail of about 6" so you can weave it in later. Bring your needle through your first stitch (I started from the bottom left-hand corner of the first "b" in the chart), around and under the base of the "v" in the stitch above.
Even if you're following a chart, take a careful look at your work now and then to see if you like how it's going, because each stitch is tedious to undo. The result, though, is pretty nice -- give it a try!