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Would have been stoked if it wasn't for the home page dropping from 5 to 5 but as we know, PR doesn't mean that much.
PR is one of the "query-independent" factors. That means it doesn't include anything about keywords in its calculation. It's more like a measure of raw "page strength" compared to all the other pages on the web, rather than compared to just pages about the same topic.
In the two years my main site existed, it moved from 0 to 4 without there being any generous linking from other websites. And in the past quarter, with me managing quite a few PR 6, PR 8 links to my site, it drops from 4 to 3..
Way to go Google..Its your choice if you want to give PR such a rubbish burial..
Even though Google has made changes to the way PR is calculated today, PR is still not the same as "ranking". It still does not, IMO, have anything to do with topics or semantic factors. There certainly are such factors in the complete Google formula - but PR isn't one of them.