SEO Weasel has an interesting theory about Link Devaluation
SEO Weasel says webmasters and website owners should stop running around like headless chickens looking at other websites for bad backlinks and links that have been devalued but instead try looking a little closer to home.
Have you got a website with a good navigation system that spreads your PR evenly throughout your site?
Do your pages rank higher than they deserve based almost solely on the fact that they have numerous internal links pointing to them?
Imagine what were to happen if your own internal links were to be devalued – Does that thought look similar to what you are experiencing now?
You haven’t been penalised, you haven’t been filtered, you are not suffering the effects of bad links, you’ve just returned to your natural organic position assuming your own links aren’t taken in to consideration as a ranking factor.