I've ridden in a skirt a few times. The skirt came to my knees and was kinda flowy. I wore cycling shorts underneath because even tho I could pull it down over my knees, the wind would catch it and even pedaling made it ride up.
When I start commuting when school starts up, I think I'll just wear my bike shorts and put my skirt in my pannier (will wear normal work clothes on top). Maybe I'm not gifted, but cycling in a skirt is hard.