The idea of storing personal information as specific as location raises privacy concerns. But Bellotti says that this is something PARC considered when developing its system. This is why text messages are only kept for a short amount of time. But ultimately, there's a trade-off between privacy and convenience, especially with this new breed of context-aware, location-based technologies. "I think people will initially accept these location-finding models when there is a big benefit to them," Bellotti says. "Once they realize that nothing bad is happening, then they may become even more comfortable with it." She likens the situation to the fact that people use credit cards for convenience even though their personal information is accessed each time they use one, and they are, in essence, leaving a digital trail behind them.

But there is still a question of how much benefit this software can actually provide. Partridge admits that the technical problems aren't completely solved yet, and there is still work to do to make the software more accurate. One of the problems, he says, is that some of the categories that people use for activities are somewhat ambiguous. For instance, "shopping" could mean going to a farmer's market, or it could mean going to Macy's. "Eating" could mean sitting down at a restaurant, grabbing a sandwich at a grocery store, or enjoying a meal at home. Partridge says that there is still work to be done to make the categories more clear, so that the recommendations will be more accurate.

Magitti raises a number of questions about how people interact with recommendation systems, says Mor Naaman, a research scientist at Yahoo. "We know people do well with recommendations from Netflix or Amazon," he says. "When you turn on a computer and it knows exactly what you're trying to do, and it gives you good information, that's the best thing in the world. It's almost like magic. But I think a lot of the trick will be in the user interface and how users perceive and interact with it. That remains to be seen in a wide deployment."

Magitti will go through public trials with young adults in Tokyo in the spring of 2008. Depending on the feedback, it might be released more broadly. The United States mobile market is another challenge entirely, says Partridge. Due to the splintered mobile market that includes various carriers and device makers, it's much more difficult to deploy a service such as Magitti here.