Google+ is open to the public, but is anyone using it?

Google+, the search engine’s attempt at social-networking, opened to the public on Tuesday as the Web giant invited all users (well, everyone 18 and up) to its service by way of a giant arrow on the Google home page. Google also announced that it has made 91 improvements to the service since its launch in June, including tweaks to search and to the “Hangouts” video chat feature.

Has interest in Google+ already crested, though? To answer that question, let’s look back to its launch at the beginning of the summer. When Mountain View unveiled this Facebook challenger on June 28th, the general consensus was that it was a pretty hip offering. Google had designed Google+ to address some of the major gripes people had with Facebook, particularly by making it easy to share updates and information with limited circles of friends, as opposed to sending pictures of your night out to college friends and employers alike.

Google+ was technically still in beta during this time – to join, you had to get a referral from a friend – and that exclusivity was part of its allure. Regardless, more than 25 million people had signed up by early August, just four weeks after its launch. (Facebook has more than 750 million users.) At the time, Google+ undoubtedly benefitted from a public backlash to Facebook’s highly-publicized privacy issues, but the new service certainly seemed to have leg.

Now, though, we’ve got some indications that enthusiasm may have cooled a bit. Developers at 89n, a web app publishing company, estimated that public messages on Google+ have dropped by 41 percent over the past two months. And as an informal indicator, it’s worth pointing out that Google cofounder and CEO Larry Page hasn’t made any public postings in more than a month. (His counterpart Sergey Brin, however, continues to post regularly. And Google noted in its blog post on Tuesday that more than a billion items are shared and received on the network every day – which suggests that Google+ is far from a ghost town).

89n collected this data through one of its services, so the figure is not necessarily a clear picture of overall activity. Not to mention, the figure does not account for private message. For all we know, Google Plus-ers are posting more than ever – but only to their close friends. However, public opinion of Google+ doesn't suggest there's any underground surge.

Opening Google+ to all users is one way for Google to stem disengagement – if, indeed, interest in Google+ has actually peaked. After all, from Google’s perspective, the worst thing that could happen to Google+ would be for people to drift away. The service might be polished to perfection, but you still wouldn’t use it if none of your friends were there, right? By throwing open the floodgates, Google stands to attract a large new influx of users, which might be just the shot in the arm its service needs to continue its assault against the Facebook juggernaut.

Are you using Google+? How do you like it compared to Facebook? Let us know in the comments.