Very little for direct traffic, but because web directories improve your ranking with search engines by providing backlinks, in the long run it will provide your site with organic traffic.
True for 99% of all directories, yep. There are only a few like Dmoz.org who are good for some really nice traffic.
is there is diference inbetwen website directory and blog directory. i understand blogs cannot be submitted to website directory and websites cannot be submitted to blog directory.. am i right.