There are three dates left to Mashable's U.S. Summer Tour 2010 — D.C. (8/5), NYC (8/9) and Chicago (8/11). The event launched July 10 in Seattle and recently made a stop in San Francisco on July 14. As many of you know, Mashable is one of the more popular sites about social media trends. For the few of you who have sent emails asking about gaining more experience in social media, this will put you face-to-face with many of the experts. So if you're near any of the cities, squeeze Mashable into your summer plans.