There have been some reports that Google bouncing new pages in search results. You can read one such story at DigitalPoint[ http://snipurl.com/geeklord200801 ]. Also, there are articles about that Google Search Algorithm Update [ http://snipurl.com/geeklord200802 ] and [ http://snipurl.com/geeklord200803 ]

If that is true then certainly the PR would matter less in SEO techniques. Also, it would be hard to keep site rank constantly high on the Google SERP for a long time.