I've been reading all the posts on Panda, and darned but some of them are "hostile", one reason why I've chosen not to participate.
I have a "theory" about what's happened, that fits the available data, and Google behavior. It's not particularly good news.
Simply put, Google has crossed the border between having manageable algorithms that are predictable and controllable to the world of uncontrollable and unpredictable algorithms, typical of super complex systems.
Super complex systems are interesting, because they are characterized by so many variables, and interactions between them (i.e. signals), that if you change any of them, the results are no longer predictable. IF you try to improve things, overall, the chances are you will make things worse, not better.
There's a point where systems become SO complex that nobody, not even the "owners" can control them. Kind of like a version of the Forbin Project.
Google has hit the wall, and so have webmasters, because no amount of fiddling will result in CONSISTENT improvements (better SERPS for Google, and better rankings for webmasters.
It's not about smarts. It's not about agendas, or even money. It's about a system that is out of control.
The implications are pretty obvious:
There's no point trying to figure out how some sites are ranked high and others not. It will be different for each site, and there are NO general rules or guides.
Blaming Google is pointless. Attributing evil motives is pointless, because even if they are perfectly intentioned, THEY don't have the capability to control their own super complex system.
SERPS will get worse and worse in terms of value for searchers. As Google tweaks and becomes even more complex, results will get worse. It's interesting that search engines that appear to operate with less complexity and fewer signals appear to be providing better results. (your mileage may vary - Google serps are not useless to me).
There are some potential solutions, and Google needs to look at them -- what they have in common is more simplification, not less. I suspect Google IS on a downward slide now. I don't see a way out so long as they try to run a search engine to index the whole web in it's entirety, because the WEB changed, but they have tried to bandaid things by adding complexity. It doesn't work.