When asked the biggest challenges in online video advertising this year, top executives at media agencies like Starcom and MediaVest say they're most eager to target audiences better and to access more sophisticated data around viewership. At last week's 4A's conference in San Francisco that drew top brass at ad agencies and brands, Daisy Whitney caught up with MediaVest's President Donna Speciale, Starcom USA CEO Lisa Donohue and 4A's Managing Director Harold Geller. Here's what they had to say about hurdles in Web video in 2010 in this week's New Media Minute. Less