Google asks not to worry about duplicate content as 30 percent of the web is duplicative. But, you don't want to have 5 pages of a website targeting the same keyword, as it can get you into the category of thin content.
However, how can you deal with short-term duplicate content, mostly put on a news site? Matt Cutts in his latest webmaster video is giving an answer to the question:
“If you had to deal with short-term duplicated content on a news site (perhaps publishing a story on two different URLs over one day), what would you do in order to avoid any penalty from a duplicate content filter”?
If it is case of high quality news publisher and you have short-term duplicate content, may be about a breaking news, Cutts recommends you to use rel=canonical tag. Even if you have multiple copies of the short stories and you will be dividing the page rank between those multiple stories or if it all this on the same topic or all the stories are on he exact same incident and they are very close to duplicate, Cutts suggests using rel=canonical to point to one home URL. This will help clarify Google that you might have some duplicate content for short-term but this is the standard spot, the preferred location on the web where you would like this information set.
As long as you do that and you don't have a huge amount of duplicate stuff all over your website, you will be in pretty good shape.Google Recommends Use of Canonical Tag to Address Small Duplicate Content Issues!,