For me, the real triumph is the hidden elastic waistband. It's smooth and lays completely flat so you don't get that sweatpant look around the middle. It looks cool on the inside, too. At first glance, it looks like a facing.
But flip it up and you'll see the secret!
One of the reasons the skirt is so easy is that it just has one pattern piece: the skirt front/back. It has a cut-on facing. You serge or zigzag the elastic to the facing and then flip it in.
P.S. The book also has a '60s inspired mini skirt version and a '40s gored, flared version!