Dive summary:

• A Nielsen study found that 42% of the people that downloaded the Foursquare app used it in July.
• There were 10.4 million people that used Foursquare in July, up 118% during the month year-over-year, only trailing Twitter's 23 million users and Facebook 78 million users for mobile apps in July.
• The Nielsen “Social Media Report 2012” study looked at Android and iPhone users.

From the article:

…Foursquare CEO Dennis Crowley addressed how retailers think about his firm's users number: "I wouldn’t say scale is an issue. But people always want to reach more folks than they are currently reaching. That’s true of any platform. It’s like, "Hey, it’d be easier to advertise in this one newspaper if everyone in the world reads this one newspaper."