According to Pew Internet Project’s September 2009 survey data, 19% of Americans tweet or use social networks to gain updates or inform others about what they are doing, up from 11% in 2008.  37% of Internet users ages 18 to 24 use Twitter or another service, up from 19% in December 2008.  Internet users who use social network sites such as MySpace, Facebook or LinkedIn are more likely to use Twitter–35% vs. 6% of those who do not use such social network sites .  More age, gender, income, education and ethnicity stats at MediaPost.