According to the Pew Research Center's Internet & American Life Project
, 35 percent of US adults have apps on their phones, but only two thirds of those who have apps actually use them -- which means that 24 percent of US adults are currently active users of mobile apps.
"An apps culture is clearly emerging among some cell phone users, particularly men and young adults," says Kristen Purcell, associate director for research at the Pew Internet Project. "Still, it is clear that this is the early stage of adoption when many cell owners do not know what their phone can do. The apps market seems somewhat ahead of a majority of adult cell phone users."
The full report can be viewed here