According to a report released yesterday by the Pew Internet & American Life, 19% of US Internet users are using Twitter or a comparable capability on a social network to update their status or follow others' status updates. This is even more true for mobile users and those who have multiple connected devices. According to the report:
Three groups of internet users are mainly responsible for driving the growth of this activity: social network website users, those who connect to the internet via mobile devices, and younger internet users – those under age 44.
In addition, 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.
These findings make sense given that mobile users are likely to be concerned about staying "connected" and multiple device owners are inclined to be "early adopters."
Does this mean that Twitter is "mainstream"? I would say not quite yet . . .