I actually prefer riding in skirts and dresses! Cooler weather is not a problem - I go with a pair of leggings by themselves or with 1-2 layers of long underwear, depending on how cold it is. For warmer weather transportation riding, I just wear unpadded (like volleyball style) bike shorts under the skirt. When my leggings inevitably get trashed, I cut the legs and instantly get a new pair of DIY bike shorts. I've also been known to wear padded shorts under a very short skirt for long rides...it just feels more appropriate if I'm out by myself and need to stop in somewhere.

I've discovered that tight skirts are okay if they're very short; otherwise, they restrict movement. Anything longer than about knee length is also a pain. Consequently, much of my wardrobe consists of skirts that are just above the knee - long enough for work, short enough for biking. I also try to avoid flimsy fabrics that require special care or are easily ruined, but this is just because I trash everything! Finally, I've learned that I actually prefer a men's style frame - I've got nothing to hide (thanks, bike shorts) and it tends to prop up slightly longer skirts and prevent them from getting greasy.