Update: Google has closed the loophole and this plugin no longer works. Please check out Automattic’s JetPack, which includes a module for auto-posting to Google Plus. This plugin works around the Google Plus block for auto-publishing by linking in through Google Voice. It gives you a way to automatically share your posts to Google Plus from the WordPress post-editing screen. It works by firing off an email to the Google Voice email address, which is then posted to Google Plus.
