Time spent on social networking sites such as Facebook, LinkedIn, Ning and Twitter jumped 82% during 2009, according to figures from Nielsen for December. These top sites have also expanded beyond the youthful audience the social networking space initially captured to find a place in older visitors’ professional lives. Facebook, LinkedIn, and Reunion.com are most popular among visitors ages 25-34, 35-49, and 55-64, respectively.  Martingale believes that this trend will continue with the emergence of relatively large niche communities like its own Toy Collector.  More on the Nielsen research here.