Regent - 10:35 pm on Jul 13, 2010 (gmt 0)
I don't typically participate in forums - rather just read them lots for information, but this Google issue seems to be an exception as I have seen this condition several times over the past several years.
Although it is just a theory, you can make of it what you want.
I started noticing this kind of Google reaction to pages that had significant content changes and about the time Google started to implement their "near-duplicate" content filtering. If page changes were modest and the keywords was relatively modest, Google would not blink. Google would re-rank the page within a few weeks depending on PR value. Higher PR values usually responded faster. But when there were more substantial changes (my experience is limited to copy changes rather than structure changes), Google would kill the page for a period of time.
My theory is that more substantial changes cause Google's near-dup content filter to re-assess the page as if it were from scratch. And as a safe guard, Google kills the page as this near-dup processing takes place. Once the near-dup processing is completed and Google is satisfied that pages have unique content, then rankings return.
Remember, this is just a theory but it has served me well for the past few years.
If Google's pattern is consistent, I would expect rankings to return within the 2-4 week period as it seems Google applies a higher priority to their near-dup content filtering process for pages with higher PR value.
But there could be complications in Google's near-dup content process. Based on some of the older Google patents covering near-dup content, PR "may" be used to assess what page receives ranking over another that is found to be in the same "cluster". If the URLs have changes and if Google is re-assessing PR values for each new URL, then other content on the web that may have near dup content could out rank the new URLs. In this case, Google could take longer to sort everything out and apply 'correct' ranking value to the new pages.
DISCLAIMER: causality and correlation are two different things. Just because I observe some correlation does not infer causality. Frogs and umbrellas have strong correlation: they both come out in the rain. frogs don't cause umbrellas and vice-versa.