We’ve heard and seen evidence that internal anchor text over-optimization (sorry, Jill, but this has really become a generally recognizable term) can result in Google penalty. Rand Fishkin, for example mentioned this issue in PRO tips as well as on the blog.
Still, while we are pretty sure, this penalty does exist, we don’t know how many internal keyword-rich links are actually too many.
Another great WebmasterWorld thread shares some results of experiments regarding this issue and while you are free to argue the overall accuracy of such tests, I thought it should definitely be brought to discussion here.
The test involved different patterns of linking from subpages to the home page which yielded the following results:
|Every site page (~90 pages) links to the home page in the sitewide nav bar using the same keyword.
|6 page drop in Google rankings.
|Every site page (~90 pages) links to the home page in-content using the same keyword.
|6 page drop in Google rankings (after the short period of improved rankings).
|Every site page (~90 pages) links to the home page in-content using variations of a keyword.
|3 page drop in Google rankings.
|The first 10 pages listed in google.com for site:domain.com links to the home page.
|Increase in Google rankings (from #5 to #3).
Just a few notes:
- As to the last point, I suspect that any 10 pages (not only those listed top 10 in Google) should be OK with Google (as long as these pages are crawled regularly and frequently enough).
- As CainIV states in the thread, the drop in rankings was easy to cope with: as soon as he removed the keyword-rich links, rankings were back (and this probably accounts for the domain trust;
- Both the effect on rankings and the penalty may largely depend on the terms: how competitive and also how “shady” they are (I imagine sudden heavy optimization for ‘poker’ related terms can result in quicker and more serious penalties).
Update: please watch this video by Matt Cutts on “over-optimization”