Are pr0 one way links to your site with good anchor good? I see tons of directories with PR5 in homepage but all the rest of site PR0... not only internal pages but also main categories are pr0, thus I guess that passes 0 page rank to all sites listed.
if it's thousands - yes, everything works if it spread across the world. if it's tens or hundreds - well, quality works better here. As for PR5 directories with PR0 categories. Don't they have some crazy names, not really connected to "directory"? I've seen many new directories set up on expired domains with high PR just for link exchange purpose.