I work in a casual office, during the week there are no suits and ties, but the guys usually sport some kind of dress pant and golf shirt/button up... There are only a couple of ladies, and we just usually wear nicer pants and a shirt or sweater... Jeans are acceptable when you have to make site visits...
Fridays - anything goes... I always have jeans, t-shirt and my pumas...
People can wear whatever they want here on Fridays, and its nice.
I dont think we need a dress code, because we dont seem to have a problem with how people dress... Mind you, I have yet to see pajamas!