The Oregonian writes about how local community wireless group turns off required ads: Personal Telco has figured out easy ways to disable the one-inch ad banners required to use MetroFi's free flavor of service in Portland, Ore. The community wireless group has been deploying free access points and zones across the town for several years, and had some friction with the city when a comprehensive plan was announced.
MetroFi offers free service with revenue coming from the screen real-estate that displays those ads. And you have to agree to view ads in order to use the free service. Otherwise, you pay $20 per month; higher tiers of for-fee service will be available, too.
As I suspected, however, the article notes that MetroFi can tell whether someone is displaying ads or not and could choose to disable users that disable ads. They're not engaging in anti-anti-ad moves yet, but could if they chose. The company says only a small number of users seem to be turning off ads, and they haven't seen a widespread problem elsewhere.
There's another way around seeing ads while you surf: Don't use the network.