Check out this article: Google revamps search, tries to think more like a person - CNN.com Google just made this annoucement today. Should be interesting.
With all the changes in Google these days the only way to ensure your rankings stick is to make sure your SEO campaigns are inline with Googles TOS, sure u can bend the rules here and there like creating loads of backlinks to your backlinks so that ur main site gets the valuable LINK juice without putting ur main site at risk but essentially Google is clear on what they want... QUALITY content, Quality Links, Link diversity and sites that are not loaded with spammy ads loads of external links...
Google is changing alot these days. Looks like they are on a mission "KILL SPAMMERS" from all around the world.
This came into my knowledge few month back and as Penguin is also here these changes will become definite.