Google announced a Public Alerts page on Jan 25. The idea is to keep you informed of emergency alerts for floods, tornadoes, winter storms, and other dangers that may be headed your way. But, it's completely query driven, not location-based in this first attempt. Google is seeking feedback. Mano Marks noted on Twitter he'd worked on this project in the past.
MapQuest launched an HTML5 client.
Adam Sadilek of the University of Rochester has developed a tool to predict one's location based on friend's locations known through Twitter. How well? It can locate you to within 100 meters with up to 85% accuracy.
"You can actually infer a lot of things about people, even though they are pretty careful about how they manage their online behaviour," he reports.