I was heavily involved in protesting the war in 2002-2003. It was definitely worth attending some of the larger rallies in DC and New York, simply for the fact that you rarely feel that sort of power in everyday life. It was amazing to be in a sea of people all united toward one goal. However, as a result of being so directly involved and then seeing what little media coverage such large events got, I no longer believe that peace rallies are effective in creating change in this society. They are more effective in less developed places, but the US has grown in sophistication to the point where a peace rally is little more than a cathartic release for those involved.
Jason