Twitter has been used to raise awareness of political topics, spread political messages and coordinate collective action.
But Twitter is also used to gauge public opinion, often producing a false sense of consensus or of how many people feel strongly about a topic (so-called Twitter storms). This is because users tend to connect with people who hold similar views to their own and are less likely to come across different issues and opinions.
By giving politicians personalised profiles similar to those of other famous people, Twitter has helped turn them into celebrities rather than public servants.
Sharon Coen, senior lecturer in media psychology, University of Salford.
Twitter data opens new horizons for scientists as a rich data source but also as a way of gathering information from the public. This has the added benefit of increasing their awareness of and participation in science. Twitter data gathering can be passive (capturing tweets that are already published) or active (asking people to take part in a project and send in information).
For example, for a project to model urban floods we asked people to tweet information about flooding near them to help us select the most accurate scenario produced by our simulations. Because this data was constantly being created we could update the model every few minutes.
Philip James, senior lecturer in geographic information systems, Newcastle University.
Twitter has opened a two-way communication between businesses and their customers. On the one hand this means it's easier for customers to complain to a company - and do so publicly. But it's also much quicker and easier for companies to reply and potentially resolve an issue, and can potentially even reduce customer support costs.
For example, in 2010, Xbox set a Guinness World Record for being the "most responsive brand on Twitter" after answering more than 5000 inquiries a day. This creates a vital indication that a company cares about its customers and so increases trust in the brand. However, high expectations can also lead to disappointment.
Twitter also creates a market research opportunity for businesses to see what customers are talking about, their sentiment and what is important to them about products and services.
And the service lets a firm's loyal customers do their marketing for them, defending and protecting the brand online and recommending it to other potential buyers.
In the example of mobile phone network outage, a network operator engaged with customers on Twitter and was able to turn around the negative event into brand advocates.
Aleksej Heinze, senior lecturer in digital business, University of Salford.
Newsrooms have long been dominated by the wires. Many journalists sit behind monitors, their eyes flicking towards the latest flashes in the corners of their screens. Twitter changed that, at least a bit. The flow of information around the world is no longer just controlled by the Associated Press or Reuters - it's being tweeted, too.
Twitter's more than 300 million users and every time a story breaks someone is there to post it, where it's shared almost instantly. For example, the first report of the raid which killed Osama bin Laden in Pakistan came from a local IT consultant.
Richard Jones, lecturer in journalism and media, University of Huddersfield.
All social media platforms are engineered to promote a culture of sharing personal information. But Twitter is unlike other sites, such as Facebook, because most of its messages are public and you can follow someone without them having to follow you back or (usually) give permission. This has created new opportunities for a form of cyberstalking that allows users to eavesdrop on personal information beyond personal and professional networks.
Twitter's highly public space means users open themselves to some of the same codes of intimacy as conventional relationships, which involves disclosure about highly personal aspects of identities, daily lives, competences and desires.
Users devise various ways to manage their privacy, for example through coded and ambiguous language. But Twitter has encouraged a new culture of connectivity based on the principle of sharing personal feelings in public. By forcing intimacy out in the open, personal relationships have been reconceived as public performances.
Deborah Chambers, professor of media and cultural studies, Newcastle University.
Twitter has changed celebrity culture beyond recognition. In the most basic sense, we are now able to follow the everyday life of a celebrity and, more importantly for many fans, communicate directly with them without strict control from their management. This means that a celebrity's image has become less about a set of fixed characteristics and more a shifting and organic performance in which the audience can participate.
Celebrities have to continuously maintain a persona that appears intimate, authentic and accessible. In some cases this really does mean instantly revealing their true thoughts in a way that wasn't previously possible.
But for other celebrities this means crafting a product designed specifically for public consumption that is as tightly managed as a magazine photoshoot. This blurred boundary has opened the way for a huge new kind of celebrity endorsement.
Kirsty Fairclough-Isaacs, senior lecturer in media and performance, University of Salford.