The original Winter Soldier hearings took place in Detroit in 1971, and involved American veteran testimonies on U.S. conduct in the war on Vietnam (including John Kerry).
According to Wikipedia,
The "Winter Soldier Investigation" was a media event sponsored by the Vietnam Veterans Against the War intended to publicize war crimes and atrocities by the United States Armed Forces and their allies in the Vietnam War. The VVAW challenged the morality and conduct of the war by showing the direct relationship between military policies and war crimes in Vietnam. The three-day gathering of 109 veterans and 16 civilians took place in Detroit, Michigan, from January 31-February 2, 1971. Discharged servicemen from each branch of military service, as well as civilian contractors, medical personnel and academics, all gave testimony about war crimes they had committed or witnessed during the years of 1963-1970.
The recent Afghanistan/Iraq War has led to a new "Winter Soldier" 2008. Full audio is accessible here.
Check out this testimony by Logan Laituri, a conscientious objector, from Truthout. Among other elements of his testimony--that his commanding officer gave a pep talk to his platoon, in which he said that they would use "dropped weapons" if there were any case of Iraq casualties that might lead to inquiry.
And here is Jason Hurd's testimony on the Rules of Engagement.
In short, these testimonies offer insights into the U.S. conduct of the war, and the effects on Iraqi civilians and on American soldiers.