Cedar Hills Crossing, a mall in Beaverton, Ore., is now covered by Wi-Fi: Access is free to visitors and the network is co-sponsored by Personal Telco.
Without interesting applications for visitors, I'm not sure how useful this network will be. I don't often carry my laptop with me when I'm shopping. There is a restaurant here that's covered, however. Plus, this would be a good place for customers to use services that let them scan bar codes and compare products and prices. Best Buy, Borders, and Office Depot are in this mall so those stores might be able to think up some useful applications for the network.
The University Village and Bellevue Square malls in the Seattle area, both somewhat upscale places, have full coverage with Cometa. But they also have individual coverage (free and fee) in individual properties throughout. It's unclear whether those two malls have seen any change in visitors or usage -- they haven't discussed it, and they may not even be able to track it.