The Denver Airport advertises “free” WiFi. Of course, it is not free. In this case, every HTTP request is intercepted by a router that replaces the response with a frameset which then loads the requested page surrounded by ads sold by the WiFi provider.
This messes any application that uses an embedded browser to deliver UI, like the Second Life Viewer, for instance.
It appears to be easily circumvented. I turned off JavaScript in Firefox and was able to view the BBC News front page without incident.