If you are talking about social media I would use Digg, Delicious, StumbleUpon to start. I would also consider going on to Linkedin (join if you have not already) and find groups that would be interested in what you are writing about. Join the groups and post in their discussion forums brief synopsis of what the columns are about along with a link. Finally, I would look for online forums and communities (like DaniWeb) and join discussion where your article topics would be relevant and promote them through the forums.
Do you mean the article directories? I think there is no need to submit to 500 or so. Submit them to the top 50 is enough, in fact 25 is enough. If you could build backlinks for these articles, that will do a great help.
Ya, your content must something useful and valuable before submitting to directories. If you are too rush in submitting your article to directories without completing and furnishing your articles, it will not be very helpful.
Submit your articles to directories which have high pr value will be useful. Go ahead and submit to all directories (maybe top 100) with high pr value (free ones will do) as there is no harm to do an extra work submitting your articles to directories which may increase your backlinks and page rank.