I find that directory submissions can be a help amongst other back linking techniques, but they are not really so helpful once you get onto or close to the first page of google.
A key issue with directory submissions is indexing, a don't have actually percentages, but it is not awesome. And even for those links that do get indexed, not all of them will stay indexed. Using a tool like backlinksindexer that Jonathan recommends here is a big help for this, but you still have the manual process of extracting the URL's from each site and then pasting them in - a tedious time suck. HOwever, paying someone $10 or something to do a dierctory submission is a small price to pay and does have some benefit.
As far as my own time goes, I prefer to spin articles and submit them to 1waylinks. IT saves time because I don't have to write lots of unique article, and even better than that the indexing rate is excellent. I checked a submission of 60 articles the other day and all of them were indexed except one, and I am sure that one is just a matter of time. You can't get any better than that for article marketing. Many mass article submission software I have used are not even close to that level of indexing.
Darren