There is much debate on directory listings having much search engine marketing value. The reason being is that oftentimes directories are not seo friendly for individual listings. A few years ago, you would see Findlaw and Lawyers.com individual pages showing up for local queries such as "Phoenix DWI Lawyer". Now that the internet is more crowded and search engine algorithms have dramatically changed, directories have lost some of their luster.
That being said, I recommmend that if a website directory is:
1. Free or minimal cost
2. Not a spam directory
3. Has a Google Page rank of at least 3
then it is worth creating a profile with your website address. It may take 5 minutes to do and it could help you.
For instance, I placed my other website, www.targetlaw.com into the free directory Brownbook. One day later the Brownbook listing showed up in a Google Alert I have for the term "Targetlaw". This means that Google must have indexed the listing and seen the word Targetlaw. Not bad for 3 minutes of work.
I will try and continue to search new directories that meet my criteria and share them with everyone.
By the way don't forget about Targetlaw, it is another free directory/search engine specifically for lawyer websites.