Google Video:
Jeff Dean talks about how Google works. Although he mentions nothing about rotating algorithms.

Google Rotating Relevancy Algorithms:
being discussed at SEW forums in this thread.

[update: NickW pointed to this post, which states that currently there are 3 main Google relevancy algorithms and that they use Agent Web Ranking to check their positioning.
McDar & WM Community also have tools that search multiple data centers at the same time.

in the SEW thread PhilC also points to a list of current active datacenter IP addresses.]

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