Great question — answering as the UphillTech team:
If you know these pages will be duplicate content then you will definitely want to make sure you tell Google not to count them as "real" pages. I would say a better option is to use canonical URLs as that is a more semantic indicator of what is going on. These pages are duplicates of an original and you're telling Google which page is the original. Plus that way even though the pages won't be listed in the search engines they should be crawled and you can benefit from the internal links structure they have to offer. If you cannot do canonical URLs then definitely block these using a noindex meta tag or HTTP header. Blocking them via robots.txt will also work.
Full answer by John Conde: https://webmasters.stackexchange.com/a/26734 (CC BY-SA 3.0).
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