arikgub - 6:11 pm on Jun 19, 2011 (gmt 0)
I would read through tedster's post about google's improved use of semantics and see whether it might related to anchor text froim inbound links.
Yes, irrelevant anchor text might be one reason, but it seems to me that even highly relevant anchor text won't affect rankings as it used before, and in general, there is some sort of shift form anchor significance to on-page prominence factors. It suddenly seems as having the right keywords in the title, or meta description, or showing closer to the top of the page really matters again ...
In the past, using different variations and combinations of "green" and "widget" in the anchor text of inbound links, was a sure way to rank your page for "green widgets" keyword. It seems to me that it has become more difficult now.