Twitter is a platform. It is just another platform where journalists have done journalism, but in 140 characters. It is certainly a whole other debate, perhaps for another committee at another time, whether a tweet is journalism. It is just a platform that journalists and other people who are interested in civic matters can use to spread information about something they are witnessing, at the time they are witnessing it, in an immediate moment.
The value-add for media is what you do with those tweets. How do you write them? Do you put more context in, or is it simply recording? As Nick mentioned, a lot of journalists, as part of their workflow, will use what they have tweeted as their notebook and go back to it to use it for their context, their quotes, etc.
It has revolutionized the industry, for sure, but it is just another platform on which we continue to try to do the work we have always done on the other platforms.