If the internet is the wild west, then Mark Zuckerberg is a cowboy who has mastered quite a bit of the terrain with 750 million visitors to his Facebook saloon. But, as seen in many old western films, there's occasionally a showdown accompanied by the cliché, "This town isn't big enough for the both of us." While Facebook hasn't met its match quite yet, Google+ may be well on its way. 

Google+ launched only two weeks ago, but in its short time on the web (and despite its invitation-only testing phase it's currently in) the social network is blowing up, and many predict that it will be a suitable rival for Facebook. 

According to Paul Allen, founder of Ancestry.com, Google+ achieved 7.3 million users on July 10. His statistical analysis also estimates that Google+ will acquire 10 million users today, and if Google keeps the invitation button active, it will reach 20 million users by this weekend. 

"My model is simple," said Allen. "I start with U.S. Census Bureau data about surname popularity in the U.S., and compare it to the number of Google+ users with each surname. I split the U.S. users from the non-U.S. users. By using a sample of 100-200 surnames, I am able to accurately estimate the total percentage of the U.S. population that has signed up for Google+. Then I use that number and a calculated ratio of U.S to non-U.S. users to generate my worldwide estimates.

"My ratio is 1 U.S. user for every 2.12 non-U.S. users. That ratio was calculated on July 4th through a laborious effort, and I haven't updated it since. That is definitely a weakness in my model that I hope to address soon. The ratio will likely change over time."

While Allen works on updating his method, Google+ continues to expand and the question on many minds is whether Google will pull the plug on the invitation button at some point or not, eventually limiting the number of users that can access the field testing phase. But whether it does or not, many current users have expressed their fondness of the fresh-faced social network.

"I predict that Google+ will go from 0 to 100,000,000 users faster than any other service in history," said Bill Gross, founder and CEO of technology incubator Idealab. "The service is great. It is timely. People are engaging with it like crazy. There are rumors that there are already 4.5 million people. That might be high. It might be as low as 1 million, or even lower, but my guess is that it's more than 1 million people already.

"The next year will tell. Will there be bumps in the road? Sure. Will Facebook and Twitter fight back with more innovation? Of course! But I'm saying that Google+ is already good enough, and the team on Google+ is being so responsive in a way that makes me believe they have a real winner here."