Is this not the entire point of Foursquare?
"It might sound weird to accuse Foursquare of collecting location data since that is the whole point of the service, but Foursquare is overstepping its bounds by constantly keeping track of their users' every move (and more) — even if they never open the app."
Plus iOS 5 introduced background support with location that did keep the GPS active and did drain the battery. Foursquare enabled it as a feature called "Radar" that was short lived due to the drain.
"This feature turns on when you opt in to Google now. "
Opt in, not opt out.
[0] Storeowners install the device, and customers have to opt-out: http://nomi.com/privacy/