As I look forward to discovering what new technologies and trends this year’s South by Southwest will usher in, I can’t help but think back on SXSW “game changers” of years past. I think it’s fair to say that no event was as momentous or enduring as the breakout of Twitter just four years ago.

Twitter launched in the summer of 2006 at a time when broadband access was spreading around the world. By March 2007, SXSW delegates were discovering the platform as an ideal way to connect with each other and share news and events tips during the festival. It’s hard to remember a time when “tweeting” wasn’t a household world, but this was the moment when Twitter went mainstream.

Four years later, Twitter still matters. The microblogging service has created a back channel between individuals and the brands, institutions and media outlets that serve them. In 2011, a company big enough to have a Chief Marketing Officer (CMO), should now be hiring a Chief Listening Officer (CLO) to not only monitor the various conversations that are taking place about their brand in real time – but to participate in them.

Twitter has also made brands more human. When a company hires someone to represent them on Twitter they can no longer hide behind their corporate logo or press release. Brands online are expected to connect with consumers in honest, unscripted ways that are breaking down the boundaries between content consumer and content creator in dozens of industries.

Facebook, by contrast, remains a closed community. Each of Facebook’s 600 million plus users decides who is part of their social network. Any information that flows in and out of this network is limited by its size and by various privacy settings.

Twitter is unbounded. When you post a statement on Twitter, anyone can find and share it with their community. This ability for random strangers to amplify and distribute a message has changed the balance of power on the Web.

We’re living in an age where a teenaged protester in a farflung country can have the same reach and clout online as a celebrity or established media outlet. Look at what’s happening in Egypt and Tunisia and Libya, where Twitter is giving disenfranchised people a voice, and a way for journalists and activists to find them. News is reported on Facebook; news breaks on Twitter.

While misinformation and clutter will always exist in such an open medium, Twitter has brought honesty and accountability back to the Web. Unlike the chat rooms and message boards that came before it, Twitter is all about connecting with like-minded strangers using your real name, not a screen name or alter ego. This in turn has helped make the Internet an extension of the physical world, a place where real business and social relationships can bloom.

Many of the friends I am looking forward to connecting with during SXSW 2011 are people I first met in this virtual marketplace. I can’t wait to find out what sort of revolutions this year’s event has in store. And I can’t wait to share them with the rest of my friends on Twitter.