Here's how you can do it yourself:
First a couple of notes 1) These directions are for a netting skirt. You can achieve a similar look with chiffon but the process is a bit different. 2) Make the netting several inches longer than the finished length--these ruffles will shorten the skirt 2 to 3 inches.
You will need netting and some monofilament. I buy the 30 lb. fishing line below.
Fold the edge of the hem around the monofilament about 1/4"
Sew along the edge and over the monofilament with a zig zag stitch. The trick is to stretch the netting as you sew. The more you stretch the netting, the more dramatic the ruffle. Just be careful not to rip the netting.
That's all there is to it! The effect is better with several layers of netting or you can go crazy and do something like this: