There has been much digression on the SEO blogosphere regarding Google updates, there is much conflicting information out there covering past methods such as the Google Dance and other monthly updates. Updates no longer take place monthly in monolithic shifts but rather as incremental updates to index, so some areas of search will vary from day to day depending on the frequency of updates there. The following blog post by Matt Cutts gives more details on the history and current updating techniques and frequency.
Tags: Google
