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If you compare the PR in directory.google.com to the PR you get with the toolbar it appears to me as if the PR in the directory has been added some credit depending on how relevant the site is for the directory it is listed in.
I have noticed several examples of this where two sites have the same PR when looked at with the toolbar, but when looked at in the directory they have a big difference in PR and the on with the highest is generally more targeted towards the category name.
The Handy Dandy Google Page Rank Figurin' Guide [searchnerd.com]
[directory.google.com...]
You will find that there is a big difference between the two and it actually looks like the ones that are receiving a high PR in the directory are more relevant to the category than the rest.