Since the latest update I've been unable to connect to a variety of public wifi sources that have a captive "portal". For some reason chrome no longer generates a "click here to login" prompt and when I try to visit to any page I get an error message "out of range". Not very useful.
The way to force chrome to display the log in screen is to visit any non-ssl site. For some reason this then prompts for a log in. Try visiting:
This will trigger the log in portal window that will allow you to connect with your Chromebook to any public network. Happy browsing.