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lazerzubb's Google Update FAQ [webmasterworld.com] is essential reading, along with the Google Knowledge Base [webmasterworld.com].
Though from what I've been seeing in the SERP's, some of the content they are still listing is about 4 months old (that's when one company that I was watching was acquired) all the current links get redirected to the new corporate owner, but it seems they are still benefiting from these old listings for the acquired, no longer existing, domain / content.