Wireless Hotspots in a Large Environment?

matth asks: "So here at work we provide wireless internet access to customers all over our city, and into suburbia, via Alvarion radio gear. We have a large number of customers that are places like pubs, libraries, restaurants, etc. We would like to, in conjunction with these locations, setup up a public Wi-Fi network. The problem is getting the mac address back through to a central authorization server. What experience have others had in setting up a Wi-Fi hotspot network over a city, and allowing a user to register at one location and get on at any of the various locales?"