When will stores start sharing (ie, selling) this info with Facebook, Google, etc. and vice versa? Stores sell mailing lists.
When you come within range of a properly configured WiFi access point, [the store] can record the wireless MAC address of your phone – a unique 12-digit number. Every time you pass by, that AP can log that number. If you enter that store or café every day, it will soon have a detailed record of when you (or at least your phone) entered and departed.
For the first time they can easily track where customers go after they enter the store. They can identify repeat customers and first timers. They can find out whether shoppers are spending a lot of time in the toy aisle but rarely visit sporting goods or home appliances, and reconfigure the store layout accordingly. They can share data across different locations – to gauge whether the same customers spend more time in their discount outlets or shop at the locations closer to major freeway exits. They can even track people who walk by the store every day but never go in, or if more people enter after a window display is changed.