Did you know that Memorial Day used to be called Decoration Day? According to wikipedia, "Many people visit cemeteries and memorials, particularly to honor those who have died in military service. Many volunteers place an American flag on each grave in national cemeteries."
Oak Hill Cemetery in Georgetown taken today (for more photographs from Oak Hill Cemetery check out this: http://www.graveimages.blogspot.com/2012/05/oak-hill-cemetery-washington-dc.html
These photos I took in 2010 at Arlington National Cemetery. Each Memorial Day Weekend, on the Thursday before, soldiers "decorate" the sacred grounds with thousands of American flags.