Nature Protocols sample workflow paper by Cytoscape Consortium - a quick overview of Cytoscape functions.
Nature Methods paper by Cytoscape Consortium - a quick overview of Cytoscape App (Plugin) universe.
Social networking services are good data sources. You can write simple web crawler using scripting languages and save it as standard data format such as GML, GraphML, or simple tab-delimited text. Cytoscape supports many standard graph file formats.
Still cannot find answer for your question? Ask your question in the mailing list.