Pleats are less ruffly, and more, well, pleaty. That is, they lie a little flatter, and are slightly less girly. Because they are flatter, they also don't require as many stitches.
I saw this version of drop stitch knitted pleats in Vogue Knitting Early Fall, in Cathy Carron's pleated tank design. It's worked from the bottom up, and only increases your cast on by 1/5.
For this sample:
Cast on 23.
Work in stocking stitch for 1 1/2 inches.
Pleat row: *K5, drop a stitch. Repeat from * until 5 stitches remain. K to end.
Gently run the dropped stitches down to the cast on edge.
