The advantage of vertical ruffles is that you don't have to cast on very many stitches. The disadvantage is that they have to be sewn on (unless you're making the ruffle into a scarf).
The ruffles themselves look like overlapping petals. You can seem them on the cover of Vogue Knitting, Early Fall 2010
Cast on 15.
*K 3 rows.
Shaping row: To shape the ruffle, you decrease all but one stitch as follows: *Put the tip of the right needle through the front of the second stitch on the left hand needle. Lift it and pass it over the first stitch on the left hand needle. Repeat from * until only 1 stitch remains on the left hand needle.
Cast on 14.
Repeat from * until the ruffle is the length you need (omitting the cast on from the last ruffle), then break the yarn and pull through the last remaining stitch
Short Row Ruffle
This garter stitch ruffle makes large circular scallops. They remind me of the large ruffles you see on flamenco dresses. A good example of this technique in action is found in 101 Designer One-Skein Wonders in the Lace Spiral Scarf.