The official Google Weblog has a good article on duplicate content
that I would encourage anyone wondering about this issue to read. In fact, I'm going to pin this post here in our SEO No-nos forum since we get this question so darn much.
Basically, they are saying the same thing we've been saying for ages. There's NO DUPLICATE CONTENT PENALTY. It's a filter so that they don't show numerous instances of the same content.
During our crawling and when serving search results, we try hard to index and show pages with distinct information. This filtering means, for instance, that if your site has articles in "regular" and "printer" versions and neither set is blocked in robots.txt or via a noindex meta tag, we'll choose one version to list. In the rare cases in which we perceive that duplicate content may be shown with intent to manipulate our rankings and deceive our users, we'll also make appropriate adjustments in the indexing and ranking of the sites involved. However, we prefer to focus on filtering rather than ranking adjustments ... so in the vast majority of cases, the worst thing that'll befall webmasters is to see the "less desired" version of a page shown in our index.
Thanks for the confirmation, Google!Hat tip to Jennifer at SEG as well.