OK, so Google has made one of many regular changes to its search algorithm, which will impact on what gets on to search engine results pages (SERPs). From casting around the web it seems the aim of the change is to penalise scraper sites and sites that do not originate content - aka content farms.
Note, this update to the algorithm affects sites in the US at the moment.
Here are some links:
The official Google announcement - Google search and search engine spam
Analysis from the SEO Theory and analysis blog
A review of the implications from Searchengineland
And here is a news feed on the announcement