Nothing. It is so simple it can be copied or recreated in an a few hours. The hard part is getting people to use it and build on it and rely on it as a busine

Nothing. It is so simple it can be copied or recreated in an a few hours. The hard part is getting people to use it and build on it and rely on it as a business. That takes years to unseat. The next twitter will have to beat it on many fronts. I believe most of twitter success was culture to allow the innovation and try (created from work at another startup odeo), timing and someone leading it that had already been through a sale to Google of blogger.com. The odds that that happens everyday isn't high. It was also the time when RESTful APIs were taking hold which Ruby on Rails had embraced, timing was huge.