Note that this is NOT http://sourceforge.net/tracker/index.php?func=detail&aid=2000164&group_id=96589&atid=615251 but I think it is considerably easier to implement :)
I tend to watch RSS feeds associated with various tags or of "user groups". For example I'm following the flickr RSS feeds for the groups "Close and Closer" and "Macro Awards".
However those feeds are overlapping quite often, containing the exactly same content with same link URL. While scrolling through the entries in the "browser area" I get to see the same content over and over again.
It would me nice to have some "Only show duplicate entries once" option for each category.