I found that Google decreased PR of my site and wonder why.
Except recent submit of my programs to download sites and change of Google Analytics to asynchronous code there were no other changes to the site I can think of.
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1) You lose incoming links
2) The incoming links you have lost PR themselves and thus "pass" less PR to you
3) Google's index increases. Since PR is relative as the index increases every page's PR goes down.
FYI, website's don't have PR. Pages do. So your home page's PR went down, not your site's.