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.
Upon further investigation of the FF plugin used for one of the ad-disabling methods, it seems likely that MetroFi would have no way of knowing the ads aren't being viewed. The plugin prevents the display of content from the specified site(s), but doesn't appear to do anything that would identify it as not accepting the ads.
Furthermore, I can't find the verbiage that requires users of the free service to, as you say, "agree to view ads" they're just there.
The more interesting news upon the launch of the network, which hasn't yet been written up, is how dismally it performed. Numerous MetroFi-Free SSID's don't appear to be connected to their network, at least not in a meaningful way (e.g. no DHCP, DHCP but unable to even bring up the splash page). The day of the launch there were reportedly only 256 addresses available for the entire network, each with a 24-hour lease rendering DHCP virtually unavailable at the time of the official wire-cutting. Packet loss on Wednesday was hovering between 40-50%, and was around 20% Thursday. Ethereal can grab all the traffic passing over the network, not just the AP it's connected to.
The simplicity of the ad delivery system, and the ease of subverting it highlight the overall impression that the system is somewhat weak and poorly designed.
You are correct that the easiest way to avoid the ads is to not use the system at all, but we had to try, if only to provide you with a story to reprint.