Not much, if we can extrapolate from just-released Pace University figures on 18-to-24-year-olds. A study by Pace and the Participatory Media Network found that, “while 99% of 18-to-24-year-olds surveyed say they have profiles on social network [sites], only 22% say they use Twitter,” CNET reports. And the researchers offered a bit of insight into how that 22% use Twitter: “85% of them follow friends [in real life, I’m assuming], 54% follow celebrities, 29% follow family members, and 29% follow companies.” I think it’s safe to extrapolate similar if not less interest on the part of tweens – at a recent conference, a Pew/Internet researcher told us teens aren’t really on Twitter. At 140 characters or less per message, Twitter’s a bit like texting, and texting – which pretty much replaced instant-messaging for youth – rules for short messages in that age bracket, I think. Pew says 77% of US 12-to-17-year-olds own a cellphone, and that percentage is growing.