From the Report’s Overview:
As of February 2012, some 15% of online adults use Twitter, and 8% do so on a typical day. Overall Twitter adoption remains steady, as the 15% of online adults who use Twitter is similar to the 13% of such adults who did so in May 2011. At the same time, the proportion of online adults who use Twitter on a typical day has doubled since May 2011 and has quadrupled since late 2010—at that point just 2% of online adults used Twitter on a typical day. The rise of smartphones might account for some of the uptick in usage because smartphone users are particularly likely to be using Twitter.
African-Americans continue to use Twitter at very high rates—28% of online African-Americans are Twitter adopters, and 13% use the service on a typical day.
Usage by young internet users (those 18-24 years old) increased dramatically over the last year, with nearly one in three now using Twitter.
Our data also suggests that these trends are deeply intertwined with mobile Twitter usage on smartphones. Fully 20% of smartphone owners use Twitter overall, and 16% use the service specifically on their cell phones.