On a tip from a reader I started up a packet sniffer before I ran a search for "Nintendo" in Dave Watanabe's Inquisitor plugin for Safari. Sure enough, the first link presented was an Amazon link, with an affiliate redirect (associate tag: exoscience).
I'm not shouting anything about the sky falling. I actually think it's great when software developers find ways to provide amazing products to users for free. This case simply raises a question of transparency. Most of us who spend any time on the 'net already know that if we click a link to a retailer from a blog or reviewer's website, there's a good chance they'll be getting a cut of any conversions. It's when those links are directly promoted by the owner and the affiliate urls are masked that it becomes a question of ethics for some.
It's certainly not required of Amazon associates that they reveal their affiliate links. But when you're providing a search service, especially when it's touted as using Google results, sticking an affiliate link in as the highest ranked result does raise some questions. Sure, we use Inquisitor of our own free will (and for free), but transparency on the part of the author would make the choice to do so a more legitimate one.