The shoe, besides being a foot covering, is a symbolic item.
During the 2003 war in Iraq, there was live television footage of people hitting pictures, statues, and effigies of Saddam Hussein with their shoes.
According to Iraqi/Arab/Eastern culture, shoes are a symbol of dirt and degradation. If you're going into someone's house or a mosque, you would always take your shoes off first. Shoes are used to beat servants, thieves, or prostitutes; it indicates servility. It literally means you regard them as dirt under your foot. If you were to beat your children, this would be done with a stick or the hand, but never shoes. Also, its considered poor protocol to cross your legs in front of others, as showing someone the underside of the shoe is an insult.
More cultural symbolism is available at http://news.bbc.co.uk/2/hi/middle_east/2934011.stm