if you're on windows chrome and hitting "plugin unresponsive" trying to join a hangout after the green room, you can hit "yes" to kill the plugin, and refresh and it should join.
a timing issue is hitting a chrome specific bug for some users. we're looking into a fix for next chrome release and a workaround in hangouts in the meantime.
Edit: this is a timing issue, and this "crash and refresh" thing fixes it for most folks who have hit it, but possibly not all... in which case. another browser might necessarily be the answer.
to know if you're hitting this bug... it seems to bite people on joining, not in creating. folks hitting this bug can create hangouts.