Dupin Users: The current version of Dupin does not accommodate iTunes 8 Genius playlists properly when they are selected for "Get Duplicates". Although I am concerned, it's probably not a big deal.
Here's the Thing: I am considering holding off the next update to Dupin (which will include the fix for Genius playlists) until some features I had been planning on adding are also implemented. While I could put up a quick fix quite soon (which would be version 1.3.5), I would only be releasing another update in a week or two with additional features (version 1.4). In either case, until the next update, you can avoid any issues with Genius playlists by not selecting them from Dupin's Playlist popup. Your "Get Duplicates" results under such circumstances will be inaccurate.