Research shows falling Facebook usage among young adults, and it could that the site has lost its cool factor. Usage data from this summer compiled by comScore shows a progressively worsening decline among 18-24 year olds. Facebook use among the demographic fell 3 percent in July 2009, then 13 percent in August and 16 percent in September. Adweek looks at the changing usage trends and says the site might be suffering the fate of MySpace, where the social net lost its cool with young adults because of a surge in use by a much younger audience. With Facebook, the problem may have more to do with attracting older adults who use the site to communicate with their children and grandchildren.