
Earlier this morning Nielsen released its latest smartphone data for the US market:
By comparison comScore says that 36% of mobile phone owners have smartphones. However the most recent comScore data show a comparable share distribution for Android and the iPhone (43.7% vs. 27.3%).
Nielsen also reported that smartphone ownership for those under 45 is much greater than the overall population: 54%. It goes even higher (62%) for those 25 to 34 years old.

The Pew Internet Project said in May of this year that 42% of US mobile users own smartphones. And in a release of new survey data yesterday, Pew found that 50% of all mobile phone users have downloaded apps (vs. 43% in May 2010). However, as we know, downloads and usage are not synonymous.
As the chart above indicates, 51% of mobile phone app downloaders use between 1 and 5 apps weekly. A substantial minority (31%) use 6 or more apps per week. Average weekly app usage is higher among tablet owners.
The following chart shows the general categories downloads by populatirty/penetration according to Pew. Curiously the most popular app download category, games, doesn't appear on this list. This is probably a flaw in Pew's survey question design.
Finally, Pew says that just under half (46%) of all app downloaders have paid for apps at some point, with most spending less than $5.