I have one, and I love it! Yes, it will fit a scarf in progress, and the yarn for the scarf, too! And maybe a little pouch for scissors, crochet hook, etc. I think they are Lantern Moon silk bags here at KH! Good price, too.
The bags are indeed Lantern Moon Silk Taffeta bags. Amazingly I can't seem to find one of Amy's in use, but the measurements are 5 inches wide x 5 inches in length and 8 inches tall. They'd most likely fit a scarf project in progress providing it's not enormous and your skein of yarn isn't too big. The bags have no pockets, just a couple of spaghetti strap handles. The fabric is very nice and shimmery. The photos don't really do them justice. They are definitely one of our number one selling products and we are constantly having to restock them.