I use Rojo.com for my RSS feeds and I will often get duplicate entries. Sometimes where there was a spelling correction/change in the title.
But sometimes I'd get several of the same entries from one source, usually Joystiq, like they don't post enough already. It's terrible to have 100 new articles but each one from Joystiq has seven duplicates.
I don't have a solution. I'm just letting you know that it isn't limited to FeedDemon.
I appreciate you sharing that information. Rojo.com is extremely impressive, I must admit. The "today" page was loaded with super interesting stuff when I went there just now. Sweet link! Thanks. And it's good--or, well, bad, if you think about it--to know that this is an issue related directly the architecture of feeds rather than my particular feedreader. Thanks for confirming that suspicion as well. Guess there really IS nothing we can do. The only solution is for the RSS/Atom standards to be updated in such a way that each feed entry can unmistakably and uniquely uniquely be identified.