Nearly 40% of Americans say they participate in online communities, with sites around hobbies, shared personal interests, and health-related issues among the most popular, according to ACNielsen. Of 1,007 respondents, 87% say they are part of a community. Of those, 66% say they participate in shared personal interest sites. Next comes hobby sites (62%), health community sites (55%), public issues sites (49%s), and commerce sites (47%). Others participate in social or business networking sites (42%), sports sites (42%), alumni sites (39%), or dating sites (23%).