submiting to free directories should get you a top pr4 ( i mean by this if you submit to quality and high pr directories ) . after that, you should get to work and look for more relevant links.
Directory submission can not hurt, and may help. It remains one part of a good promotion campaign. I don't think that it is a good idea to use it as the only way to get inbounds to your site. Keep it looking natural. If your site is truely popular, the SE's would expect to see it in some good directories.
I think yes, Recently i have seen my friends blog with Pagerank 2 only due to backlinks from directories !!