analytic tools out there to measure everything from web traffic, social interactions, mentions, and many other things for platforms like Facebook, Twitter, and LinkedIn. With Google+ being so new and having no API the large firms have not incorporated it into their current tools.
Google+ Statistics by the crew at TNW, and CircleCount by everygain have emerged to fill the void. Both offer similar statistics that they cull from the Google Profiles submitted by users. Because there is no open format they only track the profiles people submit to them. I prefer the UI of Google+ Statistics over CircleCount, but CircleCount has more users in their database. Google+ Statistics even offers a nice widget to put on your website. Be sure to submit yourself to both sites.