Well I think after some time it could be happen as google is the only place where people went to search I mean the 90% of internet users lets say if they start using google + as a social network then this could happen.
Facebook has a great portfoliow of users and the management of the Facebook making progress dy by dy to stay for staying on 1 postion. On the other hand if we look the progress Google plus have made in the last year. This is outstanding progress and they has achieve huge number of user in past year. As I think, now this year in not for Google plus and Facebook, Now this is the time to Pintrest to Grow.
@suniverm, it won't... facebook has a very strong foundation and lots of data. google has to do something groundbreaking in order to win... (maybe buy a majority of their company)... Besides what are the odds of a G+ user not having an FB account?
It's possible, I think whoever has the best service at the right time will come out on top, think about Instagram, people seem to love taking pictures these days and that grew like mad. So in a few years there will be a new craze, Google might capture it first and succeed, or Facebook users get bored and migrate.
I think that Google plus will not beat the Facebook. Google plus has made impressive progress in the last year, but it is hard to contine with that progress. Because they have a competation with the Pinterest and other big social media sites.