Recently one of my sites got hit badly. Main revenue for this site is purely adsense and it came down from $51/day to $0.40. It was having 412 KWs in semrush and I was ranking no. 2 for main KW (2 words) which is also in EMD.
I was on page one for couple of KWs. Site was averaging $15-$30/day. But when I came no. 10 for one word KW it was having $40-$50/day. But it lasted for 3 days and after that ranking for all the KWs dropped to page 6 and above in big G. And it's still the same. I was having 12K+ unique visitors in July 2011 and now in August it's 4604.
$51 to $0.40:
We were doing normal link building using article directories and blog networks like UAW etc. The main KW I was on 2nd position since Nov. 2010 and that KW is on page 6 now. I was not able to figure it out that what happened for this drop. But we still keep on doing the link building as per normal and my rankings in Bing and Yahoo improved. Due to that I am back to $15-$20/day for this site but rankings in big G are still same and no improvement.
After one month I was checking my another site 2 days back and in that site also I was on first page 2nd position for 2 words KW and also on first 5 in one word KW and I was having 20+ KWs in first 2 pages of big G. I was dominating these positions for last 20+ months. No link building was going on for this site at all for last few months and yesterday suddenly all the rankings disappeared and same thing happened like my other site. Then only I realized my mistake.
I was having 3 hosting accounts and in one of the hosting accounts I was having sites participating in networks like ABC, ALN etc. I consolidated all of them to one place in last week of July. I was having different IPs for these sites. And my main sites are having dedicated IP and name server. I thought there should not be a problem. But these IPs belongs to same IP pool and same provider. 3 days back when I created a new PR3 blog to join to ALN, I posted one of our articles and linked back to the 2nd site I am having. This is the only link posted for this site in last few months and yesterday all the rankings dropped. So far I can say that because link to my site is going from another site on the same IP pool and that is why this happened. I might be wrong but so far nothing else is pointing to this change because all other sites are having better rankings and they don't have any link from my sites on the blog networks.
If any other warrior has similar experience or would like to share some points to bring the rankings back, that will be helpful.