Talk about a topsy turvy season in the social media and tech industries.

Beyond Steve Jobs’ retirement and next week’s unveiling of the iPhone 5, the big Amazon announcement today, and, of course, the Facebook changes, there’s Google+, the social network that weeks ago seemed bound for the island of failed Google ideas.

Now the site’s traffic and membership are surging.

According to widely reported data from Experian Hitwise, Google+ saw 1,269 percent growth last week after dropping its invite-only status and opening the social network to the public. It is now the third-largest site in Experian’s ranking of social networks and forums, according to Experian Research Director Heather Dougherty.

Google+ also grabbed about 15 million U.S. visits last week, pushing it to No. 8 on the list of most-visited social networks, up from No. 54 the week prior.

Membership has seen a boost, too. According to a model developed by Paul Allen, the Ancestry.com founder who is now an unofficial statistician for Google+, the number of users had reached 43.4 million on Sept. 22, up from 28.7 million on Sept. 9.

Perhaps most notably is the shift in Google+ user, noted by Experian’s Dougherty. In a blog post, she writes:

“The evolution of Google+’s audience composition from its launch in early July to last week illustrates how quickly the cycle from ‘Innovator’ and ‘Early Adopter’ phase, to the ‘Early Majority’ and ‘Late Majority’ can occur.”

Although users considered “early adopters” still account for a large part of Google+’s traffic, the site saw increases among middle-income Americans, single people, and Hispanics, according to Dougherty.

If the interest and growth continues, brands will have a robust audience with which to engage once Google allows companies to start creating pages, something it has forbid since the social network’s launch in July, with two exceptions (Ford and GM).

A Google employee said the brand pages will likely debut this fall.

Recent upgrades have made the site more attractive for PR and marketing pros.

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