Of course, now comes the hard part: Developing Google+ in a manner that leads it to attain a critical mass of users and makes it a real contender to Facebook.

Although Page expressed much excitement on Thursday about the fact that Google+ now has topped 40 million members, success is far from certain.

After all, Facebook has more than 800 million members, and its growth shows no sign of slowing down -- on the contrary. And since the launch of Google+, Facebook has been aggressively rolling out new and upgraded features.

Some industry observers have pointed out that Google+ needs features that give it a marked differentiation from Facebook, such as unique functionality that is compelling enough to prompt hundreds of millions of people to make it their preferred social network.

This week, a Google engineer named Steve Yegge mistakenly published publicly a post in which he leveled some sharp criticism at Google+, calling it "a knee-jerk reaction, a study in short-term thinking" in large part because it lacks a strong developer platform.