Where are you?

Facebook has launched a new feature called Places that helps mobile phone users broadcast their whereabouts and track their friends: They can see who else 'checked into' a museum, shop, park or theater, what they did there and what they thought of it.

Facebook's Silicon Valley rival Google Inc. has already staked a claim with its own location service and is in the process of building a social networking service to compete with Facebook rumored to be called Google Me. Both companies are keenly pursuing the potentially lucrative location-based market, which remains largely up for grabs.

Advertisers are eager to target consumers based on their location by sending coupons or special offers to people near specific stores, bars, movie theaters and restaurants. That mobile advertising market could grow to $3 billion by 2014, up from $200 million this year, the consulting firm Borrell Associates predicts. But checking in has not yet become mainstream. Forrester Research reports that only 4% of adults in the United States use location services.

Beware: Places is far better in terms of protecting user privacy than previous new feature roll outs such as the Instant Personalization service launched in April. Nevertheless, Places can still reveal important data about you if you don't take the time to adjust your privacy settings.

If you're not convinced that posting your location can be a bad thing, check out PleaseRobMe for some evidence.

Details on how to protect yourself here.