This site was bringing in $1-2K a month so I really wanted that traffic back. So for about 12 months I tried all kinds of things to get the site to start ranking again because I knew what it could do but I eventually gave up because nothing made a difference. I put the site on the back burner an paid almost no attention to it for another year.
Then about five months ago after two years in the Google black hole I was looking a statcounter overview for all my sites and noticed that this site had zero traffic for 3 days.
While it lost most traffic, it did not lose 100% of traffic. I went to the site and it was completely crashed. The site was so far off my radar it took me 3 days to notice. I rebooted the site later that day and the NEXT DAY the site started getting 3000 hits per day.
Moral of the story: The last thing you did is not always the cause of the effect. Every time a site gets dropped, filtered, or banned, chances are you just did some kind of change if it is a fairly active site you are always trying to improve. So there will frequently be an "I did this and my site got hit" story.
The weird thing is I did nothing to my site for a year except have it crash for 3 days and it came back. I write this off to pure coincidence.
(Or you could always try turning off your site for 3 days and turn it back on to magically get all your traffic back :) )