Farida Vis is the lead social media researcher on a team that studied 2.6M tweets sent during the UK riots. The project, 'Reading the Riots on Twitter' (led by Professor Rob Procter) is a collaboration with The Guardian newspaper and Twitter. At Lift12 she gave a detailed and documented account of what happened. You will see that the early conclusions governing bodies jumped to are not very accurate...
The data visualisation documenting the rumours that circulated on Twitter at the time, built by The Guardian Interactive team (led by Alastair Dant) has recently won a Data Journalism Award for the category data visualisation and storytelling (national/international). The full visualisation can be seen here: http://www.guardian.co.uk/uk/interactive/2011/dec/07/london-riots-twitter.
Have a look at the slides: slidesha.re/RTRTlift12