I've said this before and I'll say it again; using Compete for quantitative traffic comparisons is flawed, particularly with social sites that utilize embeddable content. Their data has been proven wrong countless times. Until recently, Compete claimed Reddit (http://siteanalytics.compete.com/reddit.com/) had less traffic than Digg (http://siteanalytics.compete.com/digg.com/).
I don't have anything against Google+. But lets hold off on the congratulatory praise until we're sure the growth is real.