See my blog on blogs
As compared to individual blogging websites, the blog directories are more usually crawled by the search engines. The blog directories structure is considered ideal for the search engines. However, search engines do not search the entire site; therefore, the blogs which are fully optimized have more chances to appear in the search results. By submitting your blogs on blogs directories your chance to get more traffic is increased. Fourth, there are large numbers of incoming links available on the blog directories and by subscribing with a very small fee you can get the option of reciprocal links.