Since Ang asked me to, I've put together this tutorial on i-cord edging, which you can see on my swatch here, and in my progess pix elsewhere on this blog:
Here's how I made this swatch -- first I'll name the i-cord steps, then give more detail on each one.
1. I-cord cast-on, bottom edge.
2. Built-in i-cord, left edge.
3. Slip stitch double-knit edge, right edge.
4. I-cord bind-off, top edge.
1. I-cord cast-on, bottom edge. Provisionally cast on 3 stitches (I use the method involving a bit of waste yarn, but not the crochet one -- just personal preference). Knit 2 rows of i-cord (knit 3 stitches, slip stitches back to left needle purl-wise, repeat). *Knit in front and back of 1st stitch, knit 2, slip 3 stitches to left needle purl-wise*, repeat from * to * for each cast-on stitch, then when you have cast on enough stitches, do 2 more rows of plain i-cord (no increase), to give enough ease for the corner of the edging.
2. Built-in i-cord, left edge. Knit to last 3 stitches, yarn to front, slip 3 purl-wise, turn, knit. This seems to give an edge with the right row gauge for garter stitch.
3. Slip stitch double-knit edge, an Annie Modesitt signature touch. See the link on her website for her "Alison" scarf for more detailed instructions. I think of it like this -- normally the 3-stitch edge would consist of 6 stitches, 3 on each side of your work. Knit those 6 stitches as follows: *K1, slip 1 with yarn in front*, repeat 2 more times. Using my swatch as an example, when completing the first row after the cast-on row, knit back to the right-hand edge of the work, pick up those three provisionally cast-on stitches, then work the edge stitches as above. This results in a nice curved edging for the lower right-hand corner. However, I found that this slip-stitch edging seemed sloppy on my garter-stitch swatch. Perhaps it was my workmanship, but my theory is that for some reason the row gauge of that edging is longer than that of the built-in i-cord. I don't know why this should be, and I had the same number of edging rows on each edge, so YMMV. For my actual sweater, I chose to do the built-in i-cord edge.
4. I-cord bind-off, top edge. Work 2 extra rows of whichever edging you are doing (I chose the left-hand i-cord edge to start from), then bind off as follows: *K2, knit 3rd i-cord stitch and 1 regular stitch together through back loops, slip the 3 stitches on your right needle to your left needle*, repeat until all stitches are bound off except 3 right-hand edge stitches. Then, for the final corner, knit 2 rows of plain i-cord, and graft the i-cord stitches to the 3 right-hand edge stitches. This last corner of mine looks kinda crappy, but it was only a swatch. [ETA -- make only 1 row for this corner before grafting, since the graft stitches are the second row, and hopefully yours will look better than this swatch.)
Note: I had originally intended to stop the edging on my Sonnet right front at the point where I had cast on the additional neckline stitches, since that edge would be seamed to the back and so should be plain, but . . . I forgot. I was planning to leave the 3 edging stitches on a holder, and then graft them to the edging stitches from the back neckline, but now I will have a little i-cord ornamental shoulder seam thing, instead.
I hope that is clear -- let me know of any questions!