There used to be a guideline about the "web directories" in Google's webmaster guidelines. Google directed webmasters to submit their sites to the link directories such as DMOZ and Yahoo Directory. Note that DMOZ is a free directory while Yahoo Directory is a paid directory. Interestingly Google is against getting paid links and one can't submit a directory to Yahoo Directory without paying a good some of money. Anyways, coming back to the point, Google wanted webmasters to submit their sites to both free and the paid directories. Now this guideline has gone. WHY?!
Well, whether the guideline about directories is there or not, I will still recommend you to submit your sites to directories because backlink is a backlink and you can get one free quality backlink from directories. Guideline about getting backlinks is still there in Google webmaster tools and I think it will be there as long as Google exist because there whole algorithm is based upon backlinks. And here is an advice, be careful while subitting to directories, specially paid ones and observe Google's trend. Don't get yourself penalized by Google. Submit to a few directories and see if your site's rankings have gone down or up or no change and then submit to other directories accordingly. Do make sure that you submit to quality directories only.