Twitter added a new feature to give users more current information based on it's aggregated behavior data. In the right hand navigation bar of the Twitter website, you will notice a new feature called "Trending." This link allows you to select from a collection of geographic regions to see popular trends. Currently, only 15 U.S. cities and five non-U.S. countries are on the "Trends" list, but it is highly likely that Twitter will expand the aggregated data tools since there is overwhelming interest.
