One way to judge the popularity of Google+ is with total user growth, and some estimates put the network at over 100 million users. Those projections indicate that Google+ could have 400+ million by the end of 2012.
Another metric is interaction with brands on the site. Google opened up Google+ to eager brands back in November of 2011, and within a week 61% of the world's top 100 brands had created pages. So there was clearly initial interest from businesses. What was left to be seen was whether or not those brands could attract followers and interact with fans effectively on the network.
In December, the number of people that following one or more of the top 100 brands on Google+ was 222,000. In February, that number has skyrocketed to 3.1 million, an increase of 1400%. In just the past two months, for example, Coca-Cola went from being in 1,800 circles to 336,000.
All of this growth is impressive, but there's one caveat. User adoption of brands on Google+ is incredibly top heavy. The top ten brands on Google+ hold all the followers (occupy the Google+ Ten!). Of the 3.1 million brand followers, 3 million are held by the top ten brands. In fact, each of the top ten by themselves have more followers that brands 11-100 combined. Check out the top ten brands on Google+ below:
It's interesting how Google ranks on that list, with only 194,000 people having added them to circles. BrightEdge points out that at least they are doing better than big brands like Microsoft, Apple, and Goldman Sachs who have yet to really join the Google+ party in a meaningful way.