As you may already know, I have always expressed interest in geo redirects for products in AMZ stores.
Amazon has launched OneLink, a new link system, that lets you link your US, UK, and CA stores to all text-related products.
Essentially, this means that if a user clicks on an AFF link in your US store and he is in the UK, provided they have a UK Amazon affect, which is the closest matching product in the Amz store in Great Britain and you will be given a credit every purchase
I do not know yet if it works on FSB, but I have the code installed in the footer of my pages and I'm waiting to see it. It certainly works on the WP-enabled blog sites associated with my FSB stores.
You can choose to have only an exact product match or a close product match.