About.com says: "Unless your hair is very fine and gets oily very quickly, try not to wash your hair too often. The natural oil working its way down the strands is actually healthy. "
Live Journal Says: "Wash every day: Fine, thin hair and most short styles. Fine hair tends to become flat and greasy-looking if left unwashed for too long, thanks to the natural oils from the scalp. Short hair can become greasy quickly, too. Pick a gentle shampoo and follow with a light conditioner -- sometimes called a detangler -- with every shower.
i have fine combo hair, so i don't have much choice but to wash my hair daily. it's either that or greasy roots and flat hair, eww. pollution also doesn't help.