At the moment it would seems way out of line to suggest that there would be four hundred million users of Google+ by the end of the year, considering that at the last count in October, there were forty million Google Plus users! But there are some predictions that show Google Plus will reach the four hundred million mark due to it gaining around 625,000 new users each day and that means if this trend continues they will get to the four hundred million easily, which is just about half of the Facebook membership!
According to Paul B. Allen, founder of Ancestry.com and Google+’s unofficial statistician;
“It may be the holidays, the TV commercials, the Android 4 sign-ups, celebrity and brand appeal, or positive word of mouth, or a combination of all these factors, but there is no question that the number of new users signing up for Google+ each day has accelerated markedly in the past several weeks,”
Source [LA Times Blogs]