Every month we have a thread that is completely dedicated to watching the Updates and SERP Changes at Google - see Google Updates and SERP Changes - July 2010 [webmasterworld.com].
And if you want to research the discussions into the past, see Google Update History [webmasterworld.com], which goes back ten years.
and some changes are so important that they get their own thread - you can find many of those discussions in the Hot Topics area [webmasterworld.com], which is always pinned to the top of this forum's index page.
