tedster - 9:17 pm on Nov 23, 2010 (gmt 0)
WRT "The Big Five" factors - overlooked there is an increasingly important SE factor: semantic clarity. When your content is sending clear semantic signals, then there's little need for Google or anyone else to do dynamic testing to find the "right" audience, the "right" query intention and so on.
It is easier to achieve semantic clarity with an all div layout - tables tend to juxtapose content in the source code that comes from various parts of the visible page, for example. Does this mean I only work with table-less layouts? Hardly, it's often not practical with an enterprise level CMS.
Still, optimizing semantic and relevance signals in the content area is an important factor in avoiding the dynamic testing that may otherwise be your site's fate.
Many sites (I dare say most site) do just fine and don't experience the kind of fluctuations that this thread is focusing on. But it is an area I'd double check if you find yourself on a severe conversion roller coaster.