 The Concept of Free Directory Submissions.
Directory submissions are an important aspect of SEO.But what direcotry owners do is to tempt people with promotional offers ,i.e paid subscription on a yearly/monthly basis,so that your website is featured in the front page and gets traffic.Later when Google updates PR and backlinks you get an extra inbound link that enables you to increase your PR.
What Google did after it conducted an Update for PR and Backlinks in the month of October was that it made it mandatory to use the Google Adsense account whether you purchase or sell a link.People purchasing a link from a directory without the use of the Adsense account will not have it counted as a backlink when Google updates it and directory owners who sold links without the adsense account would have their ISP'S banned from Google.
Now for those who are going in for free submissions.It makes no sense to do bulk submissions when you know that it would take up indefinite amount of time to get the reviewal of a moderator and then get the approval.What one should do is to opt for a category that one relates too and has the minimum amount of submissions.Say you have 10 keywords and you relate well to them ,but you prefer 2 amongst them.So even if the prefered category has a greater number of submissions pending,it would be wise to skip the category and opt for another term that you relate too.This helps,since the category with lesser number of pending reviewals will have the submission reviewed quickly compared to a category that has a greater number of submission pending.
My personal opinion is for those who are into free submission opt for social bookmarking or networking sites.These sites have maximum traffic and in that case if your content/article whatever you post is appealing and is of quality your visitor/traffic rate will improve. | 
