An interesting finding. During the latest PR update Google has clearly given no PageRank to the 'General Directory' category of Dmoz, Yahoo Directory and Google's own directory (not even cached).

At present, general directories rely heavily on linking between each other. But if none of them have any links from the top 3 major directories this could potentially "cut-off the power" which fuelled the network.

Google obviously wants to halt the major surge in general directories that exist at present, and perhaps most importantly the weight they are passing on to other sites. If you have relied heavily on directory links in the past this will most likely affect your ranking since most directories will now have less power.