Chrome: If you're a Google+ user and want access to notifications and the ability to post or respond to your circles without having to switch to a Google site, this Surplus extension will do the trick.
From the extension dropdown, you can view recent notifications and add people from those notifications to your circles. There's also a sharing button for creating a new post, complete with photo, video, and link inserts (unfortunately, though, the extension doesn't pull the URL from your current tab). If you'd like to post to your Google+ circles from anywhere on the web, Surplus is a handy extension.
Surplus [Chrome Web Store]