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However, even if Google distinguishes between these pages, a part of the PR is tranferred to your regular pages since the 'new page' www.widgets.com/?source=XYZ is connected to other pages of your site.
If the content changes between the times that Google fetches the two URLs, then you should get two different (but almost identical) listings. This splits the PageRank, but fortunately Google's results clustering prevents you from having more than two listings from the same domain in the top ten.
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doc_z beat me to it