@ OP
I am not sure what you are talking about - PR or SERP!
But one thing is certain that - Google is not sitting IDLE and changing its algo for both PR and SERP almost every minute.
The theories/tricks that have been used by SEO experts seem no longer working these days. Gone are the days when webmasters could easily manipulate PR and SERP. Its hard time for webmasters and SEOs nowadays.
Ofcourse big companies will always remain there - with thousands of niche sites made to support their main site. But for that one really need to be big with big $$$.