Who will be the next Twitter?

I just came back from a conference, and the word twitter and tweet was overused to a high degree. I believe that Twitter is going to join the exclusive club of High Traffic of MySpace, Youtube, Facebook, Meembo, Yahoo, Digg, Flickr, and Google. The real question, who is next? It will have to be new and simple, as any of these projects have shown, they at first only have 1 feature, either telling you status or sharing a picture or video. It is surprising google hasn't made a Flickr killer, maybe they want Yahoo to survive, and have a community of internet gurus. I think the next member of Web 2.0 will be on mobile sites being converted to online sites. I think Food has to be explored, and local events calender site that tells you what is going down in your zip code. Similar to Craigslist, but only one mission.