Okay, this is a hot discussion. I think first and foremost everyone needs to realize one thing.
Google hasn't send anyone a notification that their site has been affected by *insert various algo updates here*.
In other words, it's all speculation about whether your site was hit by Panda, Penguin, ATF update, EMD, Freshness Algo or any one of the 10,000 monthly algo updates that happen.
So given that we don't know EXACTLY the algo, we can be assured that it's one of them. Why? Because the other search engines (I think) are getting the proper authority or ownership of the content. Or at least better than GooG.
So, to summarize, the kiss of death is to make an assumption that it's Panda etc. We should start talking about the how's and why's of evaporated organic traffic.
The reason I mention this is because before people go blowing up a site, there must first be a loss of ranking in Google. My personal 2012 guide book is to see if one of these black holes out there sucked up the ownership of my own content. If that didn't happen, then perhaps I look into what my site might be doing wrong.
These are asinine discussions ultimately. I for one assumed Panda. Actually twice. Once? Well jeez it was a penalty (manual) where I swore that it happened during a Panda update. Wrong and about 12 months of misery that I had because of misdiagnosis. My second nightmare has turned out to be because a site actually took ownership of my site/content and now I'm delegated to "omitted results" only in GooG. Again, I thought Panda. Is it really Panda?
The point is nobody here, no experts or self proclaimed SEO gods can really say for sure what you're suffering from. Part of diagnosing is determining whether this is a GooG only issue. That might help you decide what or whether to pursue.
The fact that I will stand by is that there is an algo issue. This is a biggie and in my opinion, it goes far beyond Panda. It's at the core of what we do. It's about who owns what and that your creations can be owned by somebody else and they can cash in on your own creations and writings. It's worse when the 90% market share algo is getting this wrong. It's a bad situation made much more worse for the average webmaster. It's called anarchy. What I see is this as a GooG exclusive. Whatever happened with all the tweaks is that more than ever copied content is outranking or simply replacing original works. Yes it's always happened. It however is predominant in GooG and not the other search engines. This isn't the way it's always been. It's the way it is now in 2012.
The only remedy here is to first be aware. Then second, fill out that damn GooG scraper outranking form. Third is to voice what you are seeing.
This is a full circle mess. People are now suggesting that your site lost authority, and therefore the scrapers outrank you. That's to suggest that you are in the wrong and that you have something to fix. It's to assume that the algo isn't a fault here. That's a damn big assumption to make. Dare I say ignorant. Let's at least consider the fact that an authority site/high PR site can take a lesser sites content, post it (or all of it) and take the rankings from the originator. It appears as simple as this. It's the only way I can explain my situation in dealing with a black hole that took away ownership from me on my own site. One example and perhaps unique, but a real example of just how bad the algo can work right now.
No one person webmaster operation is going to spend their life submitting DMCA notices and fighting scrapers. That's endless, tiring and futile. If the other search engine is doing something better on this, then the fact is they are more webmaster friendly. No other way to say it. When an algo can incorrectly let other people widely outrank original content, you have a serious and horrible situation for a lot of us. Almost a close shop situation.