Their are many variables that can determine the value of any link to your site and
PR is not among the most important. Yes most directories have a high
PR on it's homepage, but very little
PR for it's category page. If so, the flow of
PR will be limited as well.
But what is more important in directory submission is to always submit to the correct category, vary your anchor text ie the title and description a bit to make it natural to Search Engines.