With the news of a Greek medal hopeful being kicked off the Olympic team hours before the open ceremony because of controversial tweets on her personal account, public figures must realize their tweets don't exist in a digital vacuum where free speech is unfettered.
From the controversies of the 'choc ice' tweets to the poorly executed attempts at humor by premiership footballers and Hollywood actors, public figures have not grasped that there are responsibilities as well as rights when comes to free speech and careless tweets are cannon fodder for news coverage. Unless public figures realize this , they will be subject to controversy likely to affect their careers and the public perception of them.
However this is bound to happen as the twitter format doesn't exactly encourage thoughtful debate. It's quite difficult to clearly articulate your position on a given issue in 140 characters. it serves as a reason why most twitters seek to be clever rather than succinct as they only have a limited amount of words to express themselves. It encourages the skills needed to write good ad copy rather than reasoned debate when addressing the public.
In sum, Public figures end up in controversy as they see twitter as a just social forum when it more than that. Twitter however, doesn't encourage reasoned debate as public figures need more than 140 characters to articulate their positions on any given event.
It encourages skills required for ad copy than addressing the public explaining why most controversies on twitter have come from public figures poorly executed attempts to be ironic. Public figures have rights to free speech, but in an age where the words they speak are under scrutiny by the media and wider public alike, their responsibilities with regard to free speech are just as important.