The number of Americans who use Twitter at least once a month remains relatively small, at 17 million, or about 7% of the total population, according technologist Erik Sass writing in The Social Graf blog.
Separate figures from Nielsen and ComScore suggest the site has been attracting an average 20-22 million unique visitors in the U.S. in the first months of 2010. In contrast, Facebook has been online twice as long and has six times the number of unique visitors.
Twitter has grabbed the imagination of a sizeable subset of professional Americans, and it has garnered a huge level of name recognition in the U.S. population with 87% of respondents to a recent Arbitron-Edison Research study saying they were aware of the site.
"This raises the question of whether Twitter can truly go "mass market" in the same way other sites like Facebook and MySpace have. Looking at the trend lines, the answer would seem to be "no," Sass writes. The chart below tells the story: