"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."

http://googlewebmastercentral.blogspot.com/2006/12/deftly-dealing-with-duplicate-content.html

[ I tried to minimize the amount of duplicate text.]

So, not only does duplicate content may risk getting the dupes removed, it also seems to add a couple of points to your "spam" threshold value... :)

Does this only apply to the majority of the content being the same?

I'm asking because Google issues duplicate content all the time with Blogger – especially now they've introduced labels. For example, a recent post of mine would exist in at least four places:

   * Home page
   * Post page
   * Archive page
   * Labels page (one for each label)

Does that count as duplicate content? According to this point, it might do:

<< Understand your CMS: Make sure you're familiar with how content is displayed on your Web site, particularly if it includes a blog, a forum, or related system that often shows the same content in multiple formats. >>

I think this point is interesting too:

<< Use TLDs: To help us serve the most appropriate version of a document, use top level domains whenever possible to handle country-specific content. We're more likely to know that .de indicates Germany-focused content, for instance, than /de or de.example.com. >>

I think (indexable) labels pages are a soft form of duplicating content. I guess it all depends on "how much is the same on each page" and "in what quantity do those pages exist." You know more about your system, but I suppose an individual labels page is not exactly the same as the post page, i.e. there's often other context to the post? Do you have an example link for each of the 4 types you mention for one of your posts?

Well, for example, this post I've just made:
http://ruscoe.net/blog/2006/12/new-gadget-nokia-n73.asp (Post page)

I decided to give it a new label of "mobile" which automatically created this page:
http://ruscoe.net/blog/labels/mobile.asp (Labels page)

Those two are almost identical (and will remain so unless I get loads of comments or label more posts with that label). Furthermore the same content also appears on these two pages:
http://ruscoe.net/blog/ (Home page)
http://ruscoe.net/blog/archive/2006_12_01_archive.asp (Archive page)

And all done using Blogger, one of Google's own tools.