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For one thing, the 'real' PR of the entire Web adds up to 1.00 to avoid the need for renormalization as the Web expands. The toolbar PR is related to the actual PR by a logarithmic function known only to Google. The toolbar PR is updated infrequently, and usually reflects your TBPR of several months ago.
Regardless, Page Rank is only one of several hundred ranking factors used to determine your page's position in the SERPs. A simple way to look at it might be, "It makes a difference if all of the other ranking factors are equal."
But I'll take the middle ground here, and say that PR is neither unimportant, nor all-important. The PR you need to out-rank your competition depends on many other factors, including (obviously) how much competition you have in your keyword sector. You will find that sites with high PR tend to over-emphasize its importance, and sites with little or no PR tend to minimize it -- a case of ascribing success to only the most visible factor in the first case, and possibly just sour grapes in the latter.