If you check in at Starbucks, it's not Starbucks that would pay to talk to you, it's McDonald's. Just like Google, if you are searching "Starbucks", it makes no sense to show a Starbucks.com ad.

An 'ad' isn't the only activity Starbucks would post. We're in a less traditional paradigm here. Starbucks can do ad-hoc market research, community building, announce products... Lots of things. Some of the other commenters build on this further through competitive analysis and predictive modeling. Over the next few years we'll see this go further as they better understand the cooperative nature of brands and likes.