LockerGnome - For over a decade, broad and comprehensive social networks like Facebook and its previously popular predecessor, MySpace, have been the predominant social networks. In the last few years, startups have been building niche social networks that offer unique features depending on users’ interests. Some of these networks are geared towards those affected by cancer, and others towards pet owners. While Facebook doesn’t look like its popularity or growth are going to slow down anytime soon, several of these other niche networks are positioned to become just as hot for those with specialized interests. Here are four new social networks to watch in 2012 — and potentially even join, too.