The community in which I live has a handy listserv. Members pass on local news, post announcements, advertise the availability of goods and services, ask questions, and offer advice. Someone looking for a reliable company to finish a basement or a veterinarian to take care of an ailing dog can get useful recommendations from neighbors who subscribe to the list.
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Facilitated by e-mail and the Internet, such social networks have grown to become important avenues for seeking information. Social networking systems, such as Orkut or LinkedIn, create online communities in which new members join by linking to friends who already belong to the system. The result is a network defined by friendships.