Bay Area startup shopkick today launched its self-titled iPhone app (free, App Store) in a bid to upstage Foursquare and other location check-in rivals. The service uses GPS to detect when it's within range of a given store and will automatically send a "signal" to a device in the store itself to let it know when the user is close. Shoppers then get credits, or kickbucks, for visiting the store that they can ultimately roll into actual discounts, even if they haven't necessarily bought items during the earlier trips.
