You can almost guarantee a PR3 or 4 the next time the update rolls around. (I say almost because G is a fickle beast). How can you do that, you ask? You just get a single link from the home page of a PR5 site. That's usually all it takes. Will it help your SERP? Probably not, unless your site is on the same topic. Then you might see a small lift. But the lift will happen weeks before the little green bar moves.
[edited by: tedster at 4:55 pm (utc) on April 5, 2009]
I think this is why over the years, SEO's have said to pay less attention to the "little green bar".
Is it fair to say however that when Google first became a major player, there WAS more of a connection between PR and SERP position? But the connection is actually less now because their algo has continually evolved? Those of you who study this more closely, please correct me if I'm wrong. I think it's the word "Rank" that makes for the confusion...