I know that everytime when Google update the
PR, quite number of site admin will found that their site
PR drop. This is because Google is keep develop the formulation of
PR calculating and review the site (Those site with ton of backlink but no content will definately "die").
IN this case,
PR no more a game, you cant get high
PR by just insert ton of backlink. You really need to concern about your content to maintain or get higher
PR.
PR still the only guide to judge the value of your site.