A succession of cautionary tales has shown the dangers of social networking

In the halcyon days of the early 2000s, when social networking still involved going to parties, the number of people you could offend with a brief electronic message was restricted to one. Nowadays, that single drunken text can be transmitted instantly to the Twitter feeds of a few thousand people – many of them itching to concoct an outrage, or spot an infidelity.

This, at least, is the recent experience of a lot of high-profile "tweeters" who should have known better. The communications giant Vodafone, for example, managed to allow one rogue worker access to the firm's Twitter account long enough to type: "VodafoneUK is fed up of dirty homo's [sic] and is going after beaver". The employee was duly suspended.

The Welsh rugby player Jonathan Thomas, meanwhile, was forced to apologise after sharing 140 characters of homophobic banter. Either he misunderstood the medium, thinking his message would be sent only to fellow Ospreys lock Ian Evans, or he misjudged the sporting climate for such a joke, following the news that his Wales team-mate Gareth Thomas is gay.

The guitarist and singer John Mayer partly blamed his excessive use of the social networking site for his break-up with actress Jennifer Aniston. It's difficult to argue that you are unavailable because you are working hard recording your new album when your girlfriend can see that you've spent half your day on the internet.

It's also not easy to project a particular tone of voice when you only have 140 characters to play around with. Free of context, many witticisms can be twisted. The journalist Giles Coren tweeted a funny (if tasteless) joke that was characterised the next day by one paper as a "'sex-death' rant".

"When you're talking to people," says Jo Bryant of etiquette guide Debrett's, "a twinkle in your eye can convey an awful lot of meaning that gets lost when you have such limited space to write something. You should always think twice when tweeting."

The biggest Twitter fail of the week fell to family man and television presenter Vernon Kaye, who was caught sending "sexy" tweets to a Page 3 girl. Kaye seemed to understand the workings of the site and kept the messages private. His mistake was to send the said messages to an employee of the UK's bestselling tabloid newspaper.

Liz Matthews, a publicist for a number of young celebrities including Alexa Chung, says Twitter is "a great promotional tool ... These days brands even ask their celebrity endorsers to tweet about the brand in their contracts." But she adds: "I advise all my clients to protect their privacy."

Another peril for famous people is online impersonation, and Matthews spends a lot of time trying to have fake Twitter accounts erased. "At the last count," she says, "there were five or six fake Alexa Chung profiles on Twitter."

This year's internet craze is expected to be "location-based" social networking such as the Foursquare service, which allows people to automatically tweet their location to their followers, and provides yet another minefield for the celebrity tweeter.

Imagine the havoc a much-followed star could cause with an innocent status update, such as "John is at the pub" – or, indeed, "Vernon is at Spearmint Rhino".