dickbaker - 8:21 pm on Feb 27, 2011 (gmt 0)
If this were the case, many sites with good content that was not materially different from other pages on the the same site or on on peer sites would drop in the rankings -- this would account for "my site is very good but I still got whacked by the new algo" comments in this thread. It would also account for some of your pages getting whacked if you have a good site, but others not getting whacked.
Interesting theory, as are many theories offered over the past few days.
Many theories, like Whoa's, assume that Google is dropping the rankings for a site that just isn't as good as the others that were ranking nearby, and that the drop in rankings was more or less benign rather than malevolent.
If that were the case, why would pages that were ranked at #5 to #10 drop all the way to #40 to #70 or, in some cases, disappear from the index entirely? (I have a couple that have gone missing). There's simply too much garbage between the #7 spot and the #70 spot for Google to be saying, "after careful consideration, this is where we think your page belongs, and these other forty or fifty sites are ones that we deem to be better."
If there isn't a return to some bit of normalcy after a few weeks, then these kind of drastic drops would appear to be more like penalties than just adjustments. A site that, like so many here, has been on the first page for years or even over a decade can't suddenly be a "bad" site deserving of punishment, after having been considered "good" for so long. There's been too many updates for such a site to have not been affected before.
I don't think we're going to know for sure if our sites are really "good" or "bad" for at least a couple of weeks. It's been that way in the past.