Tonearm - 7:10 am on Sep 6, 2012 (gmt 0)
Are you a backlink builder?
Have you been building links on (high PR) non-relevant sites?
I've never done any link-building whatsoever besides a DMOZ link many years ago.
What type of changes are we talking about? Not sure if you meant a benefit to users or you've actually benefited from a traffic increase (huge, no less). But since this sounds like some dramatic changes have been done, it would seem reasonable to look at those as a potential culprit. The timing is also right.
So, what did you do?
I removed repetitive keywords, unlinked keywords from anchor text, and reduced duplication between the titles, descriptions, and headings of various pages.
Erm if your traffic is unaffected, and going up, tis possible you caught your ranking on a down period, rankings do fluctuate, and its unlikely that your visitors are seeing the same rankings as you
I think the Piwik data I posted above indicates my visitors are probably seeing the same ranking I am for this keyword.
This may the issue. To some degree, to de-optimize is to optimize. And if you de-optimized a perfectly optimized site that was already ranking well, then a ranking drop might be expected. Also, if the site was stale and you made sudden changes to the text, it could cause a ranking drop. I have personally witnessed this. You didn't state specifically if your site was stale, so I am just suggesting it as a possibility.
Did your rankings drop for all keywords, or just this one? If it's just this one, that doesn't match up with what I've seen in the past when a penalty hits. I'm not saying it's impossible, but it seems unlikely that only one page would suffer.
It actually doesn't seem to be the page. The keyword is "widgets". My second highest-traffic keyword is "purple widgets" and I'm currently #1 for that keyword. Both keywords relate to my widgets.html page.
Welcome to your new glass ceiling, Tonearm, and if you improve your sites aggregate rating (google secret sauce type stuff) you will enjoy continued success with Google.
Would Google implement a glass ceiling by dropping the rank of a high-traffic keyword by 4 pages?
What's the overall traffic doing?
Overall traffic is way up since I de-optimized which was shortly before I noticed the ranking drop for this keyword.