Had we moved forward with it, we would have needed to find a way to store MAC addresses anonymously. Because these days, it's entirely too easy for third-parties to seek or sell "business records" to be correlated. Can you just imagine if every CCTV in your city also logged your phone's Wi-Fi Mac?
For those of you interested in running an experiment, check out March's Linux Journal: Wi-Fi Mini Honeypot
But do be careful on what you collect, and how — it's a dangerously unregulated landscape.