I had a twitter account in 2006/7 when it was still a project management tool and half my team at PWC were based in US so we sort of tried to use for work but it was mostly talking with other elearning type people elsewhere and it was a big time for Second Life so lots of virtual world experimenting taking precedence.
Have repeatedly come off and on it since then. Like Facebook.
When Twitter is sold at the end of the year probably to Google, with Microsoft owning LinkedIn, it is a death of how social betworks online will function. No matter what these US companies do (emperors and nightingales).
Whether a new free open source Twitter takes off, remains to be seen. Or whether other social networks outside of these familiar ones evolve into something different online (longer term).
Finding more and more that people are sick of their ideas being stolen by others in developed countries who are connected with specific political influence at the time.