Video is the fastest-growing online advertising format with estimates of about a 40-percent growth rate through 2010. And the marketers that have taken part in its growth are resoundingly satisfied, according to a recent study from video ad network BrightRoll. More than 50 percent of the agency executives who participated in the study indicated that online video was the most effective form of advertising, and 83 percent said they were getting more value for their video advertising spend in early 2010 than the previous year.