Two already doing it; three more by the end of the month. They identify location to within a few meters; smoothing algorithms can turn this into a path through the venue.

The technology can tell when people enter a shopping centre, what stores they visit, how long they remain there, and what route they take as they walked around.

They indicate but do not identify; that is, a signal is unique but not (yet) connected to identifying personal data, they claim. However, they use the IMEI of the handset to index users, and that provides a pivot into unique identification, which the reporter failed to be horrified at:

In the case of Gunwharf Quays, managers were surprised to discover that an unusually high percentage of visitors were German - the receivers can tell in which country each phone is registered - which led to the management translating the instructions in the car park.

How fortunate for those German tourists, who now have parking instructions in their native language. Technology is great!

Via Times Online.