Quadrille - 11:15 pm on Jul 16, 2008 (gmt 0)

It's a common affiliate problem, but Amazon have been pushing it as a matter of policy:

Once upon a time, Amazon encouraged affiliates to use their own content with simple 'individula item' links for buyers; over the years, Amazon have encourage affiliates to use more and more 'pre digested content', with the inevitable duplication issue, which Amazon wins over their many thousands of affiliates.

I've stuck to the original system; it does not convert as well as it did, as the number of affiliates has grown, but it still works. And no dupe issues.