About 19% of all U.S. internet users say they use Twitter or another instant status update service to let their friends know what they are doing at any given time, according to a recent Pew Internet & American Life study. This is up from 11% over previous surveys in Dec. ‘09 and April ‘09. Women are slightly more inclined to use such services, as are people aged 18-29. In fact, 3 groups of users are mainly responsible for driving its growth - social network website users, those who connect to the internet via mobile devices, and younger internet users (under age 44) the more devices someone owns, the more likely they are to use Twitter or another service to update their status. Fully 39% of internet users with four or more internet-connected devices (such as a laptop, cell phone, game console, or Kindle) use Twitter, compared to 28% of internet users with three devices, 19% of internet users with two devices, and 10% of internet users with one device The median age of a Twitter user is 31, which has remained stable over the past year The median age for MySpace is now 26, down from 27 in May 2008 The the median age for LinkedIn is now 39, down from 40 Facebook, however, continues to gray: its median age is now 33, up from 26 in May 2008