Well, you probably already know about the new Google update. While the last several updates don’t have a distinctive name, this past update which came roaring in during March and April wreaking havoc to all SEO’s deserves a name like a great storm- this one named “Dewey” after a code word used in Matt Cutt’s blog. Following is some of the information I have been able to collect on Dewey, hopefully giving SEO’s information that can be useful for their clients and websites.
The Dewey update has ruined many spammy sites.
1) Old sites that have bought paid links suddenly dropped down Google's index around the end of February, early March. This seems to be particularly affecting thin affiliate sites.
2) Cache data has been inaccurate and appallingly unrefreshed even though the index reports that new content and links are working. Which is probably due to the delay with which an update gets rolled out accross the multiple data centers.
3) New sites take an excruciatingly long time be indexed whereas up until late February/early March it was a fairly quick and painless process. We have seen clients crawler activity diminish. Googlebot seems slot to drop out the old URLs as well.
4) Site: queries don't match up with inurl: queries. There doesn't seem to be a tremendous amount of consistency in the number of results returned based on queries that should return the same number. Less relevant results have floated to the top of many queries because more relevant pages have either dropped out of the index or have been penalized for having most of their inbound links being reciprocal or paid.
Many directories have fallen off the map as well. I would recommend comparing your rankings in multiple data centers using the SEO chat tool. one more thing that domain name values are diminished the links pointing to them that use unbranded keywords are not therefore a domain like cars.com continues to have value because people will link to it using the unbranded keyword "cars".
Hope this update help you in understanding goolgle Algo.