Here's info on the latest Google algorithm change, Directly from Matt Cutts:
"I just wanted to give a quick update on one thing I mentioned in my search engine spam post.
My post mentioned that "we're evaluating multiple changes that should help drive spam levels even lower, including one change that primarily affects sites that copy others' content and sites with low levels of original content." That change was approved at our weekly quality launch meeting last Thursday and launched earlier this week.
This was a pretty targeted launch: slightly over 2% of queries change in some way, but less than half a percent of search results change enough that someone might really notice. The net effect is that searchers are more likely to see the sites that wrote the original content rather than a site that scraped or copied the original site's content."