If you are developing a Google Hangout App, don't be surprised if you press the "Enter a hangout in developer sandbox" link and get an ugly 404 error. Take the resulting URL, that looks like:
grab the GID (in my case 110709744297), and form the URL:
and now you're back testing again. (last night I had an update for AnywhereBoardGames, and was greeted by this nasty surprise).