jdMorgan - 4:32 pm on Jun 27, 2010 (gmt 0)
The old reports of the results of "shocking" Googlebot indicate a recovery time ranging over five or six days up to nine months, with the time depending on how often your pages are spidered, previous keyword and 'trust' rankings, inbound link strength and diversity, and many other factors.
I haven't done any "mass changes" in several years now, but I suspect that the longer recovery times have been reduced -- mainly because of a much smaller number of 'disaster reports' being posted here at WebmasterWorld.
How big of a shock was this? -- How many pages are we talking about here?
You mentioned that you did not change the HTML page headers. Did the page content change? Did the linking structure change at all?
What do you plan to do if recovery takes ten days? - a month? - several months? -- I don't normally recommend 'backing out' big changes but for the sake of discussion, how reversible are your changes? How separable are these changes -- e.g. the CSS vs. compression aspects?