we can only rely on guidelines... http://www.google.com/support/webmasters/bin/answer.py?answer=35769
You can't find the google algorithm update, it's google's secret. But if you read a lot seo tutorials about google, maybe you will get some idea.
You can find Google update assumptions on different forums/channels like http://forums.digitalpoint.com. As far as the change is concern then Google officially announce about the change after each update on their blog or you can find it at Matt Cutts' (a SEO specialist at Google) blog.