According to the latest data from the Pew Internet & American Life project, 15% of online adults in the U.S. now say that they have used Twitter in the past and 8% told Pew that they do so on a typical day.

Overall Twitter usage has actually remained pretty stable since early 2011 (the slight changes over the last year are safely within the margin of error). What has changed, though, is the number of daily active users, which increased from 4% in May 2011 to 8% today.

Sadly, the Pew report doesn’t delve into the details of how exactly people are “using” Twitter. It would be interesting to know, for example, how many people use it to just keep up with status updates from others and how many actually post to it.

As for the demographics of today’s Twitter users, the data has also remained relatively stable lately. African-Americans continue to use Twitter at very high rates, with 28% saying that they have used it in the past and 13% using it daily.

Young adults use Twitter at twice the rate of those between 30 and 49 (26% vs. 14%) and urban and suburban residents are more likely to use Twitter than Internet users in rural areas.

Twitter usage among young adults is one of the few areas where there have been significant changes lately. Since May 2011, daily usage of Twitter among those 18 to 24 increased from 9% to 20%, a trend the Pew report attributes to the increasing popularity of smartphones among this group. Smartphone users, after all, are far more likely to use Twitter daily than those with feature phones (13% vs. 3%).