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BR
a lot of people have mentioned amazon and ebay results showing up in the serps recently. some put it down to an increased ability on google's part to spider dynamic content, others to a more spider friendly restructuring of the sites themselves, or changes to their affiliate programs such that PR is passed through affiliate links.
all are possibilities, but if it seems that news stories and message boards are showing up more also, increased ability to spider dynamic content is the most logical explanation.