Decentralised, cell-based resistance seems to be proving a more worthy adversary than American military strategists had anticipated, according to this war update from the Washington Post (free registration). According to V Corps commander General William S. Wallace "the enemy we're fighting is different from the one we'd war-gamed against." From the article:
Enemy gunners on rooftops and balconies had apparently been alerted to the approaching helicopters by dozens of cell phone calls made by a network of observers, the sources said. "We're dealing with a country in which everybody has a weapon, and when they fire them all in the air at the same time, it's tough," Wallace said.