"When your little Hogwart checks out the latest Harry Potter book at Amazon, he or she may be reminded that they've already ordered the book. It's all part of CEO Jeff Bezos latest patent for the Contextual presentation of information about related orders during browsing of an electronic catalog, which also covers warning customers about drug interactions ('you previously purchased Drug ABC'). The USPTO allowed the patent after four years and five rejections."
You can't blame Amazon from trying hard to grab what it can. It is the system (US Patent and Trademark Office) which is screwy.
This is the same sort of stuff that Microsoft's 'Clippy' offers - "It looks like you are writing a letter...". Yet again Amazon gain a monopoly on some relatively obvious aspect of online selling. Now the burden shifts to everyone else - you need to hire a phalanx of your own lawyers to ensure you don't infringe on Amazon's patents. It's probably one of the reasons why Australian online bookstores are lame compared to Amazon.
Read the slashdot thread. This is lunacy.