I was in the neighbourhood, so I stopped by Concord Cafe, since their node was reported on the auth server as being down for two months. Bell “upgraded” their DSL connection, and gave them a fancy new modem+router+wifi (it's white and thin, kind of like an airport extreme). That device had detected the presence of another router on the network and had, essentially, disabled it. Users who logged into wirelesstoronto would see the portal page, but from then on all HTTP requests would be routed to a nonexistent URL. To disable this nonsense, I had to use their desktop to connect to the Bell router's web interface, and a dialogue popped up explaining that there's another router on the network, and do i want to keep it disabled? When I went into the Bell router's web interface, I couldn't find the “disable other routers” option – I wouldn't know where to find it again if the dialogue didn't pop up. So everything's working now.