But the proper use of quotation marks isn't limited to whether to use them to avoid claims of plagiarism. A recent news story from my alma mater (Northwestern's Medill School of Journalism) focused on another aspect related to using quotation marks -- the use of unattributed quotes.
The issue came to my attention when a fellow Medill alum e-mailed me a recent article from the Chicago Tribune. The Trib article focused on the use of unattributed quotes by Dean of the journalism school in the Letter from the Dean column that appeared in the Spring 2007 issue of the Medill alumni magazine.
Apparently, a columnist (David Spett) on the Daily Northwestern (the student newspaper) found the quotes curious (they didn't sound like something students would say) and so he: 1) tried to find out who might have said them, and 2) took the Dean to task for using unattributed quotes -- a technique that Medill students wouldn't get away with in class. The Trib article highlights the issue well (as well as some some of the politics that might be further fueling the controversy).
Given that this was a letter from the Dean that ran in an alumni magazine, I don't think the use of quotation marks should be analyzed in terms of the strict rules a journalist would apply to a news story. Instead, I would analyze it this way: in choosing to use quotation marks the Dean was trying to add credence to his opening statement that Medill is producing well trained students.
Clearly, he could have made the same point by simply saying that the feedback he's gotten from students confirms that they feel well trained, etc. But, because he chose to use quotation marks he clearly was implying that it's not just his view and so readers should have been told who else, specifically, supports his claim (if for no other reason, so that readers can decide for themselves whether the persons quoted are believable, etc.).
I think the bottom line is that quotation marks are a very powerful tool and should be used with great care.