Hi Activitysuper,
I can speak to this matter in some degree. All directories are not bad, paid or otherwise.
Quick history, before panda, penguin updates a link was a link was a link, the ones that passed the most juice were high page rank, with the least amount of other outgoing links. If for any reason a site was bad, the links it was linking to were simply ignored or passing no juice.This wasn't that long ago mind you.
What happened is what always happens when money is involved, people starting manipulating the hell out of this. Directory owners started artificially pumping up their page ranks by creating elaborate link rings and exchange programs, once they reached pagerank 4+ they could then sell you a paid listing for big bucks. And it was actually worth it (if you don't mind the grey area) because you would get the link juice and a bump in your page rank as well. On top of this any place that allowed for users to post links were getting spammed.
Google swept in with their swift hand of justice and deemed many of these directories as spam, and further punished sites that were spamming their links all over the place.
So today you look at directories and you do have to wonder should I list there. The answer is very easy. Look at the directory, does this look like a place you would visit for information about your industry? If the answer is no, you don't need to be there.
Some examples of good directories from my industry.
<cite>www.efunda.com/</cite>
www.globalspec.com/
www.saeglobalsuppliermarketplace.com
www.eng-tips.com/
www.thomasnet.com/
www.yahoo.com
www.dmoz.org
What is all comes down to is:
Does the directory offer something of value to the industry?
Does it look like a place where I would search for something in my industry?
Are my competitors there?
If you said yes, to any 2 of those then you probably should be there.