Why won't ubuntu on a wireless internet connection work with Panera bread or other hotspots

Why won't ubuntu on a wireless internet connection work with Panera bread or other hotspots

I currently am running Ubuntu 9.04 and have a wireless card installed with the correct driver. When I try to connect to a public hotspot sometimes the connection works and sometimes it doesn't. Do these public hotspots use some kind of proxy that isn't compatible with the wireless card?