Ryan Cavanagh, Data Analyst with Chitika Insights provides this analysis of the short-term impact of Google+ opening itself for public registration.
Like most following the progress of Google+, Chitika Insights questioned whether the move to make their site public worked out in their favor.
According to Microsoft Co-Founder Paul Allen, Google+ went from 28.7 to 37.8 million users, coming with a 30% growth over two days of being made public. He also believes that their current number is closer to 43 million.
Our team of data analysts recently looked into Google+'s total share of traffic in our servers to see if we could see this "explosion" of growth that many have been talking about.
Insights observed over two weeks of Google+ traffic, and while there were certainly spikes, traffic tended to fluctuate despite the influx of users. This most likely means that Google+ doesn't do a good enough job at keeping users on the site regularly, and though they have a growing user base, usage of the site itself is still the same.
I've attached two graphs to this email, one showing the two-week share of traffic, and the other showing a cleaner rolling average so you can see the progress they've made since making their site public.