According to the Pew Internet & American Life Project, Twitter usage has risen to 13% of US internet users in May 2011, up 62.5% (from 8% in fall 2010) as reported by eMarketer. It’s clear that Twitter usage is still growing, but for a service with a high level of awareness among the population, it still has surprisingly few users.

According to data from Arbitron and Edison Research (of U.S. consumers in general):

• 92% of Americans are aware of Twitter, but only 8% of consumers ages 12 and up have ever used it
• Awareness of Twitter increased 5 percentage points, from 87% in 2010
• Usage of Twitter increased only 1 percentage point, from 7% in 2010
• Awareness of Facebook is also higher than usage – more people have heard of Facebook than use the internet in the US – but the gap is not as large, with 42% of consumers using Facebook (according to an eMarketer estimate)

After laying out the numbers, eMarketer concludes that “Twitter has thus far failed to make its value proposition appealing to most Americans who have heard of it.”

Will 2011 be the year that Twitter usage really takes off in the US, or will it continue this steady (but slow) growth pattern?