Aaron Wall put up a post about a new Google filter that causes people with high ranking terms to be bumped down to position #6. There is also a thread at Webmaster World about this phenomenon. This is still reasonably speculative in nature, but there are a lot of people who have seen this.

Aaron offers some really interesting speculation about why this may be occurring. The most interesting theory was the notion that it was an anchor text problem. Here is what Aaron had to say:

I think this issue is likely tied to a stagnant link profile with a too tightly aligned anchor text profile, with the anchor text being overly-optimized when compared against competing sites.

Whether or not this is occurring now, this makes complete sense. It is well within Google’s (or any other search engine’s) ability to detect an unusually high density of one form of anchor text to a given domain. For example, if your site is called yourdomain.com, and you sell widgets, and the anchor text in 48 or your 65 links says “Widgets on Sale”, this is not natural.

Most of the links to your site should be the name of your domain itself (i.e. in this example, “yourdomain”). Such a distribution of anchor text is a flag that the anchor text of your links are being artificially influenced. How is that done? Why by purchasing links, or by heavy duty link swapping...

This one has been around for a while but has now moved on to older sites... generally making sure you have the odd new inbound link holds it off.

Too many links with the same anchor text doesn't look natural. That's why Google doesn't like it.
I try not to use the same anchor text too often.

lol... it is all about random surfer theory.... too much repetition of anchor text suggests manipulation... not everyone uses the same words - though actual domain names are an exception and reason why they do so well.