This is proven and tested. during the time I started blogging, I always use my imprtant keywords as my anchor texts in my articles, advertising in free ad forums and even in signatures... becauese I have a lot of new keywords that needs to be promoted recently, I missed to maintain those previous keywords I had.. Example alone are the keywords "social bookmark sites" and "top social bookmarks"... I had my site moving up and down on number 3 and number 5 positions (may to June) with these keywords. I stopped promoting these keywords and also stopped using them as my anchor texts and in just 3 weeks, my ranking fell to page 8 to page 10 of google... I noticed this when I checked my ranking and I was upset seeing my competitors on top... I submitted 2 articles to 3 directories and used the keywords again to mig sig and after just 1 week, I am regaining my positions... Though my current position is at the biottom, I am sure I can fully regain my previous position or even higher if I do a little more submissions... if you want to maintain your position, you must also monitor your competitor's.....