The secret to Web 2.0: what do Flickr, Ning, Kiko, Vimeo, Shadows, YouTube, Furl, NewsGator, Shutterfly, Mefeedia, Feedster, Planzo, Zazzle, Tailrank, Yakalike, Qoop, Lulu, Blish, Flagr, FireAnt, Odeo, Measure Map, EVDB, Gather, Oyogi, Last.fm...