I had given up on directory submissions as they seemed to make little impact. Then one day I had a large order and tracked it back to a listing of mine in a small, low traffic directory. I then started to see various sales tracked back to directories.
Seeing that it appeared some people are actually using the directories for what they are intended (to find info) I renewed my interest in them.
One sale per 100 directory submissions per year. Times this by thousands of submissions, well, the math talks.