dvduval - 6:21 pm on Sep 3, 2010 (gmt 0)
One theory I offer is google seems to be assigning a trust/pagerank score to domains now and then they are qualified for so many "keyword points". Then basically you are going to get traffic from a limited number of keywords based on your score.
I'll bet you also are finding you are seeing fewer new keywords, and a larger swath of google traffic is coming from the same keywords.
As far as directories are concerned, things like the anchor text of the link pointing to your site should still have a positive effect in most cases. I still recommend hand submitting to directories so you see exactly where you are submitting. When you just pay someone to submit it "approaches" more the idea of "paid links". But when you hand submit, you are playing a role in the quality control.