Plazes, as with other emerging location-tracking services, has a number of obstacles to overcome. To start, the Plazes community is relatively small, with fewer than 100,000 active users. The more users a service has, the more likely there will be relevant information about a larger number of places. While Petersen says that Plazes is growing, the number of users is tiny compared with online communities such as Facebook (which has tens of millions of users) and MySpace (which has hundreds of millions of users).

Another hurdle is balancing privacy. "There are worries about privacy in all the systems," says Yahoo's Naaman. "There's obviously risk in sharing location with the public or even other people." He says that best practices for such systems need to be established so that people have a better understanding of how much they can and should disclose, and to whom.

Plazes's approach to privacy, says Petersen, is to let users determine if their locations are public and which friends can see them. In addition, people must manually "plaze" themselves in order for others to know where they are. "People publish their locations," he says. "They have to initiate it."

Petersen notes that he and his team are still looking to make Plazes more user-friendly. In the coming months, people will be able to update their location using e-mail and instant-messaging tools, he says. Also, the company will experiment with location-based advertising--a sort of "AdSense for the real world," says Petersen. He envisions landing at an airport, posting his location, and getting updates on rental-car deals or coupons for services that he used when he was last in town. Plazes can provide a fine-grained level of filtering so that ads can be targeted precisely, he says. At that point, "it's not advertising anymore: it's information."