Of online adults, 13 percent use Twitter—up from 8 percent in November 2010.
The study, which can be found here, also reveals some interesting stats about Twitter use and minorities. The Twitter adoption gap between African-Americans and whites has increased over the past six months, according to the study:
African Americans and Latinos continue to have high rates of adoption of the service. Fully 25 percent of online African Americans use Twitter at least occasionally, with 11 percent doing so on a typical day.