Ok, so for me personally - I have worked out what has happened with regards to my rankings. This may not be correct for you - but this is, from what I can see, has happened to my sites, and it is simple.
I do SEO for my own site and I have 4 clients who I do SEO for. Thankfully the sites I do SEO for did not get affected - only my site did. And not only that, for my site not all of my keywords got affected - only some.
All sites have solid on site SEO, all sites have (fairly) solid anchor text diversity and all sites have solid link diversity. The ONLY difference between my 4 clients sites and my site, and the only difference between the keywords that got affected and the keywords that did not was simply; the quality of the backlinks.
For my site before I got into the SEO game I used a super shit SEO company in India. They gave me a lot of unrelated spammy backlinks. For example, for the keywords that were in the top 10 and are now not anywhere to be seen I had lots of blog comments from angry birds forums! Lol.
It is almost like G has seen my site have lots of shit backlinks for one specific keyword, then canceled all the juice going to my site for that keyword, so now for that keyword only I am not ranking.
My backlinking strategy for the sites that have not been affected is simply creating lots of Web2.0's with good content and keeping them alive by posting in them once a month, video posts, PDF shares and powerpoint video shares. I then backlink them with niche forum blog posts, SeNuke, Rss feed and then ping and tribepro. So, this is what I am going to continue to do.
My lesson learnt - do it yourself - don't trust anyone to do quality backlinking for you!
Also food for thought, in a way Google is winning, the new 'blackhat' is flooding the web with really good quality content. Surely now, everyone is a winner.