That would probably be in breach of Amazon's affiliate policies though, IIRC editing other peoples links (replacing codes, or adding yours to a link that has no affiliate code) is frowned upon and a reasons to have your account closed.
As this is providing extra links rather than changing existing ones, it shouldn't be against Amazon's rules.
I'll no doubt irritate Google though as it could affect their ad revenue. I wonder if it would be possible to detect this sort of thing: implementing some sort of checksum on the content they send out and checking it with client-side script to tell the user that the page had been modified. It would flag up changes some users are expecting (from deliberately written/installed add-ons or greasemnokey scripts, and would not be able to identify the source of the change, so it wouldn't be perfect. And of course add-ins changing the page could just remove the checking code - but that would be a nice big red sign to say never trust a line of code released by this company/person again and would be an arms race (though Google probably has the resources to keep the upper hand in that).
