They're pretty young, for one thing. Though 13-to-24-year-olds represent only 15% of Internet users, they make up 35% of "active online video viewers," according to a new Forrester Research report cited by eMarketer.com. These active viewers "are highly engaged with online video, paying attention to longer programming and the ads that run with it," Forrester says. I'm sure they're among the Web's most active video producers too. For more on this, check out the charts on eMarketer's summary page.