It’s a big misconception - having duplicate content does NOT mean your domain will definitely be penalized!  Need proof?  Just check the all the huge news sites: CNN, Reuters, Yahoo, etc. They all publish news from the same agency sources.

If Google finds a duplicate, it will be ranked worse than the version considered to be the original. That’s all, it’s not a sitewide, general domain penalty.

If you overdo it, especially if there is a lot of duplicates on the same domain, then you could trigger a real penalty that may affect the whole domain.  However, in order to do this, you would have to really go overboard.  The only time I could see this happening would be an auto-blog that grabs content from other sites and constantly gets complained about.

Duplicate content is much less evil than most people think.  (Getting it ranked well is another story.) If you are duplicating content only to have more content availible for visitors while publishing your own content as well, I think you’ll be fine.