What do you think 'public interest' means?

http://www.guardian.co.uk/commentisfree/2012/may/15/public-interest-open-door

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What defines the public interest? It is an issue that has been behind many of the arguments at the Leveson inquiry. It's an important principle that can be used to defend journalistic activities that go beyond what is normally considered acceptable behaviour – such as the use of subterfuge – to obtain a story, where complex moral and legal arguments are at stake. However, it is also often stretched to cover activities that many find thoroughly objectionable, not even of interest to the public.

What do you think should be the definition of the public interest, what kind of issues should it cover and what is wrong with the present way it is used? As the Guardian's readers' editor, I am writing an Open Door column next week about this issue, and may use some of your examples.