Planet13 - 9:28 pm on Feb 13, 2012 (gmt 0)
I copied the first few words from my index page and I appear in the number 1 spot.
...for the index page, one of the keywords hasnt even lost position while 99% of them dropped back.
If you Google search our title with spaces in it and without the tld we show up at number 5 which makes me think there is a filter in place.
We are a pr5 site 150k back-links that has taken years to build.
Hopefully some of the moderators will jump in here, but putting these four things together, I think there might be some keyword-level penalty in place against your site.
You said that your site title shows up at number 5. does your site title have one or more of the keywords in it that lost position in the SERPs?
What does the anchor text in your backlinks look like? Is it primarily an exact match for the keywords for which you are trying to rank?
Also, what type of link building did you do? How natural are the 150K backlinks to your site?
Also, how diverse is the anchor text for the INTERNAL linking on your site? Does the INTERNAL linking use all exact match for the keywords?
Again, if you have triple checked that the technical errors are all taken care of (including the canonical errors), then personally, I would look at the inbound links and the internal linking being over optimized. (Maybe someone blasted your site with exact match spammy links?)
But that is one man's opinion, so hopefully others will chime in here.