Recently Twitter announced their wide international customers, but Twitter is not the only social networking services in the planet earth. I believe you still remember (MySpace). MySpace was launched in August 2003, it was a dynasty by it self it has had no competitors. however, they couldn't last for long, then came several social networking till Facebook came into the surface. by that time MySpace has lost its popularity. Regardless, what happened with MySpace they still function and competition still around, but staying of course for the better innovation, and ideas. Thus, for twitter to stay around it should learn the mistakes others have done till know and keep up with every new Advertisement technology.
by it self plus IPO and other features that Facebook have.