There is a search engine conference SES New York happening Feb/Mar 2006. Duplicate content is one of the seminar topics.
I have just posted on webproworld following dutter's comments about the session:
http://www.webproworld.com/viewtopic.php?t=61246
All the normal issues of having one url for any one page were mentioned. But of particular interest was a link to a pdf slide presentation about
Duplicates. It mentioned work on looking at documents and finding how many words would be required to be removed to make one document the same as another = Shingles concept. How many documents were "Near Duplicate" with small amounts of dynamic content.
This is certainly very interesting with trying to make say an articles, or affiliate site like Amazon - where you are taking content that is copied many times around the web, and trying to make your page specifically unique. You need to make sure that you are adding enough unique information to get around such filters. Not just adding several words in titles, meta descriptions, and opening paragraphs. This sort of filter makes it increasingly difficult to get copied pages unique, and increasingly harder when someone copies your page to make sure that your page is not considered duplicate, therefore not shown on the search engines.