Over the past few days I've been finding a new player showing up in the rankings under my favorite topic.
The "new player" however is simply a self proclaimed new search engine that goes out and copies existing forum posts and stores them under different categories. When you search, you get nothing but forum topics.
When I google the exact search terms used for any given page the site doesn't rank at all for that topic, which is usually the title of a post somewhere. So far so good, you'd expect it to be buried since it's 100% duplicate.
Whats weird is that although a given page is deeply buried for it's title it ranks extremely well for random long tail phrases commonly found in various forum posts.
Example, in a forum about widgets it may be common to say "big blue widgets" and this site would NOT show up for that term under its page titled "big blue widgets" but almost always a page with a completely different subject that has the words "big blue widget" in it is showing up top 5 for "big blue widget".
I think what's changed is the way relatively new sites are indexed and ranked. What we called the supplemental index in the past seems to be replaced by a few different factors for assessing sites nand pages, especially age and backlink "burstiness".
Duplicate filtering seems to apply unevenly across that set of factors right now, and situations such as you describe can take advantage of the holes that have been opened up. I haven't taken time to nail down the particulars - I'm pretty sure this situation will not last.
If you feel there is a widespread problem in a group of SERPs, you can use Google's official channels to report the specifics. They are detailed in the Google Forum Charter [webmasterworld.com]