A student who racially abused footballer Fabrice Muamba received a 56 day sentence in March 2012 …
lThe same month as a law student was given 2 years community service after pleading guilty to racially abusing ex-footballer Stan Collymore on Twitter.
Lord McAlpine is suing 500 Twitter users for tweeting he was a paedophile (he's offering to let users with less than 500 followers off if they donate £25 to Children in Need). He's suing Sally Bercow for £50,000 damages
See David Conn's analysis of an official report into the racism and other abuse footballers and clubs have received on Twitter and other social media.
Another tweeter was arrested in July 2012 for messages about Tom Daley's late father.
Back in August 2012 The Guardian published a list of 10 ways in which Twitter users could find themselves in court.
The case that perhaps best demonstrates how far the police are prepared to get involved over tweets concerns a joke, but was no laughing matter for the tweeter involved, who was found guilty and faced jail after 3 trials, but finally won his freedom after his third appeal succeeded at the High Court and his conviction was quashed.
Here's some resources to help you explore this case, gather 5 key facts, and 5 specific arguments for and/or against his conviction:
Lets start with the Wiki on the case!
(Now former) Tory MP Louise Mensch condemns the prosecution;
More reaction to the ruling;
After the publicity the case recieved, the legal guidelines on when to prosecute social media users was altered to prevent unnecessary prosecutions in future - here's a BBC summary.
There are yet more Guardian articles here, or simply try googling 'twitter joke trial' with additional search terms.