“11% of online American adults said they used a service like Twitter or another service that allowed them to share updates about themselves or to see the updates of others.”
“Twitter users are overwhelmingly young. However, unlike the majority of other applications with a similarly large percentage of youth, Twitter use is not dominated by the youngest of young adults. Indeed, the median age of a Twitter user is 31. In comparison, the median age of a MySpace user is 27, Facebook user is 26 and LinkedIn user is 40.” (note: emphasis mine)
“More than three-quarters (76%) of Twitter users use the internet wirelessly – either on a laptop with a wireless connection, or via PDA, handheld or cell phone. In comparison, 57% of those who go online but do not use Twitter, and 59% of internet users as a whole connect to the internet wirelessly.”
See the full report, Twitter & Status Updating, Feb 12, 2009
2/27 Update: Just discovered this slideshare deck that visualizes this report.