After an impressive month of explosive growth, reaching 20 million users in three weeks, Google+'s traffic numbers are falling, Bloomberg reports. Total Google+ visits fell 3 percent in the fourth week since its launch; the week before that Google+ visits had risen 283 percent. Fewer new users is bad news for a site that hopes to beat Facebook's 750 million mark. But perhaps even more worrying, average time spent on the site declined from five minutes to 15 seconds, meaning the millions who have accounts don't really use them.

Initially, Google enticed users onto the site. They made it seem like a privilege to have an invite. They wowed the tech community with their privacy settings and circles. But the allure of a shiny new social network has worn off, argues TechCrunch's MG Siegler.

Part of it was the new car smell, but a bigger part was that expectations were so low for what Google would come up with in the social space (their own doing). When Google exceeded those expectations, people were genuinely surprised. And that also spurred usage. There was a sense of excitement: Could this really be the next big social network?

But now things are calming down. The new car smell is wearing off. And it’s time for reality.

Sure, lots of people have Google+, but visiting the site isn't that fun. "Google gave users a compelling reason to sign up, now they need to provide a compelling reason for coming back. That’s a lot easier said than done. Just ask Twitter. User retention is a bitch," explains Siegler. People may have given up because the social network just doesn't have enough social yet, argues PCWorld's Juan Carlos Perez. "With Google+, because of the limited availability, it may be that after checking it out and setting up a basic profile, existing members aren't finding enough reasons to return because a critical mass of their friends aren't on it yet."

And the interactions that do happen on the site, at least for Siegler, don't make him want to come back.

After initially checking it several times a day, I now load Google+ about twice a day, mainly to see if I’m missing anything. I rarely find that I am. I +1 a few things here and there, maybe leave a comment. But overall, the content feels fairly stale. Almost everything shared remains about Google (or worse, Google+ itself).

While Google doesn't have limited resources, like other Internet start-ups, getting users and keeping them is still important for the social network, they only have one chance to make a first impression, Siegler argues.

During these first few weeks, Google+ has also weathered a few controversies--one involving allowing users to use names other than their real ones, and another in which they kicked off business profiles. While the network came out of these alive, certainly the bad moves turned some users turned away from the site, argues Perez.

Yet, the data comes with a few caveats, and Google doesn't think it should start freaking out quite yet. A third party site, Experian Hitwise, which tracks Web traffic (not the official Google metric) calculated the numbers. Google cautioned that the measurement is based on visitors and not users, and that third party metrics don't factor in mobile usage and navigation bar, reports CNET's Steve Musil. Additionally, the data is U.S. only and Google+ is technically still in Beta, Siegler reminds critics. But, for Siegler, the specifics don't matter all that much. "Still, the trend is the important thing: traffic is down week to week."