You’re strolling down a boutique-lined street. A restaurant catches your eye. You whip out your phone, scan the bar code on the window then go online to peak at reviews. It got raves so why not go in? After all, you’ll get a ring on your phone if your parking meter runs low whilst you’re dining. Then you can pay for more time – by phone. These are just two of the mobile phone location-based scenarios that have launched here in San Francisco. More to come.

We’ve come a long way since Howard Rheingold first wrote about Smart Mobs. The U.S. still lags behind some countries in the proliferation of uses for cell phones. Soon we’ll see a flood of location-based services (and ads?!) for those out shopping or exploring, according to Geographical Sciences professor, Paul Torrens, who is studying crowd behavior.

“Crowds of shoppers, endowed with smart chip credit cards and RFID tagged merchandise are trailed by long-lasting data shadows that follow them ubiquitously. Embedded in urban infrastructure and in the very products we consume, new technologies are emerging to enable cities to think about—and process—the people that pulse through them, with a burgeoning code-space being developed to capture the actions and interactions of individuals within large dynamic crowds.”

Recall soccer fans’ post-match riots? Notice the apparent increase of teen and tweens’ cyber bullying and other tragically belittling behavior via computer, texting and Twittering? Now staging flash mobs from a distance and anonymously, using technology, can create havoc and/or change opinions almost as quickly as inciting a riot at a stadium.

And one can attract larger crowds. People don’t even have to know each other to gather. They can literally take their rage and revenge to the streets faster, armed with the right location-based technology. They can swarm to surround a victim with less forethought and more speed.

In short the stakes are higher, for good and bad location-based crowd behavior now. The flip side of this sometimes lethal, tech-supported action is the ability to swarm to a location to play, protest or even surround people who in danger – a human ring of protection. For buying products, collaborating, sharing opinions – and so much more – the trend toward technology-supported, location-based services will probably touch your mobile life.

That’s why I wanted to interview the far-sighted, thoughtful Howard Rheingold.