Although the use of HTML and early Web browsers expanded the Internet - perience from mostly one-to-one interactions to that of one-to-many (massive publishing), this development still did not a?ord the sophisticated kinds of - cial interactions undertaken by people in the real world. Recently, however, new technologies(suchasWeblogs, Webservices, Websyndication, taggingwithfo- sonomies, and Wikis), sometimes collectively called Web 2.0 technologies, have appeared that o?er more socially oriented network interactions. This has led to the new system development mode of (a) employing lightweight scripting l- guages to bundle various Web 2.0 elements, or plugins, and then (b) deploying them on network servers, thereby establishing social network systems (SNS). The physical nature of the new network architectures is increasingly hete- geneous, comprising more lightweight portable devices (cell phones and PDAs) interacting with ever-more powerful multi-core network servers that host SNS. Emerging from these developments arepopular services such as Facebook, M- pace, Friendster, LiveJournal, Flickr, and YouTube. These sites employ tagging so that people can ?nd others with similar tastes and share media ?les stored on theservers.However, analystsandobserverspredictthatSNShavemuchgreater potential than merely exchanging media ?les; they are expected to a?ord opp- tunities to meet and engagein extended, creative, and more meaningful (in fact, unforeseeable) interactions that will greatly enhance the end-user experien