Google+ Manager adds a slew of keyboard shortcuts that give you immediate access to the functions of Google+.
It also embeds an icon to the right of your user name on the black Google Bar. Click it, and a menu opens listing 10 category sections (e.g. Home, Profile, Photos, Circles, etc.), which will take you to that part of your Google+ account. This is handy if you're using another Google service, like Gmail or Google Docs, where the Google Bar appears along the top of the browser window, so you can jump to a specific part of Google+.
Is a post in your Stream written in a language you don't understand? Google+ Manager appends every post with a "Translate" option, which will convert the text to another language.
Google+ Manager is also available as a Firefox add-on https://addons.mozilla.org/en-US/firefox/addon/google-manager/.