47% of US smartphone owners used shopping apps in June 2012

"Ebay and Amazon are beating social commerce platforms like Groupon and LivingSocial in the mobile shopping app contest. According to Nielsen, eBay Mobile - which allows shoppers to take photos of items to list for sale and notifies them of auctions and watched item status - attracted 13.2 million users in June. That's an increase of 31 percent since January 2012, according to Nielsen data provided to ClickZ.
Those eBay users spent more than an hour with the mobile app in June, far more time than all but one of the other apps in the top 10 list. The only app that beat eBay in time spent was mobile shopping rewards app Shopkick, which boasts a whopping three hours and 19 minutes in average time spent in June. Still, the Shopkick app user base is only around half that of the top three shopping apps - 6.5 million uniques.
Amazon Mobile and Groupon round out the top three shopping apps by unique audience in June. Interesting to note is the growth rates of the apps. While eBay grew 31 percent since January and Amazon rose 35 percent to 12.1 million, Groupon's unique audience grew only 10 percent according to Nielsen, reaching just under 12 million unique users.
According to Nielsen, 47 percent of smartphone owners in the U.S. used shopping apps in June, accessing them 17 times on average in that month."

Source:  Clickz, 7th August 2012