Read here about duplicate content on google.com: http://www.google.com/support/webmasters/bin/answer.py?answer=66359
agree. duplicate content is spamming. Google tries hard to index and show pages with distinct information.
Well, Google simply hates duplicate content. Although there is no penalty for duplicate content because Google has not algorithm to decide the authorship of the content yet. It consider few factors to judge the authorship but still there are loopholes in this whole process, - Content which get discovered first will considered as original;l - Website with high PR will get the credit of content, in case same content is appearing on multiple URLs - Content with authorship tag is considered as real author of the content In case Google finds duplicate content on duplicate content, it will filter all the duplicate pages from SERP and rank only one page.
Google is all about having unique quality content on the web, so duplicate content sites are pushed down to the bottom of the pile or de-indexed altogether
Duplicate contents are duplicate, so no use. That's why Google don't give them any importance. That's it.