walkman - 4:45 am on Oct 15, 2011 (gmt 0)
IMHO bouncing in and out is not as big as Google not ranking your site any higher than position 150. Personally I feel its a much louder message from Google that they will not rank your homepage higher than page 15.
Sounds like your site has Panda Fever. Unpredictable and wild swings are common with Panda, even with well established but poorly branded sites.
Goodroi, it's Panda . My site would not rank for a certain term anywhere better than 180 when I checked after Panda. Then it was 500 and then disappeared. Since September I'm in the 30-50 range. Totally insane, totally Panda, totally Google, totally ruining people's lively-hoods.
My term would be the equivalent of "Advice for Webmasters" for this site, last link added with that was years ago and only 3-4 mention it so it wasn't over-optimizing at all. Hundreds of other links are with "domain name" or domainname.com since it makes sense.