Google seems to have tweaked its search engine algorithm  a bit to further fight low quality content and online spam. Panda algorithm v4 seems to make sites with poor quality content even more difficult to find (thus improving your search experience as a user). [info found in SearchEngineLand]

SearchEngineLand also reports that Paydat Loan Algorithm v2 was also released attacking "very spammy queries".

It is believed the Panda update impacted 7.5% of all english language search results.

The moral of the story is to stop using blackhat or greyhat SEO techniques and to start relying on real value added content to drive your rankings.