At present the most common way to value a directory is to look at its toolbar PR. Everybody agrees that this is not a good way to value a directory, but all the other ways require so much more work that most simple stick to this very inadequate measuring stick. 

Here are what I consider to be the 2 key core parameters that should be measured:

1. the qualified traffic a listing would directly provide your site with.

2. the qualified traffic that a listing would provide indirectly through better search engine ranking thanks to the back link.

Everyone will agree with what I have said so far! The disagreements start to come as we try to drill down and work out how to quantify these 2 parameters. The first is reasonably simple. Future traffic is not measurable today. It’s a guess, and the directory owner will not tell you how much traffic the directory is sending out in a particular category or subcategory. So this first parameter can only be measured after spending time and or money on submitting your site.

What is useful is if you have more than one site, try a directory, and if you see traffic coming your way thanks to the submission remember that directory!

Since the first parameter is not quantifiable it’s the second parameter were all the action is at. PR of the linking page, quality of the surrounding sites, quality of the directory as a whole, number of inbound links, …. there are a lot of possible factors to measure. That’s why toolbar PR is the way at the moment to classify directories.

Any other way is a LOT of work. So not having the time nor inclination to spend so much time on this I went to my bookmarks and pulled out the following site:

http://www.seomoz.org/tools/page-strength.php

It would be great if someone decided to use this tool for measuring directories.

I have to do some submitting shortly for this site, and I may do it for a limited list.