Amazon.com have "Context Links" in Beta release. With this system you add a few lines of code to a web page and Amazon automatically inserts links to products in their catalog. If someone buys the product, you get a commission. This is an extra feature in their affiliate program.
I tried Context Links on my own Blog and on the ACS Digital Library, with limited success. On one of my travel web pages, Amazon put in a link from "Eurostar" to a European train travel guide, which made sense. But it also put in a link from "ICE" to a novel about a frozen wasteland (ICE is the German high speed train). This was a forgivable error.
On the ACS Digital Library it put in a link to a subscription which could be purchased on Amazon for one of the journals. Strictly speaking this was correct, but it was a surprise to those of us organizing the publication, as we didn't know subscriptions were for sale on Amazon. Far worse was that it put in links to books by authors with the same name as ones who wrote in the library and to books which happen to have the same names as papers. This makes the facility essentially useless for use in serious scholarly writing.
Context Links also put some odd links on my Blog. For an entry about environmental building in Canberra, it linked the word "Canberra" to a set of papers for a conference held in Canberra.
Compounding the problem of the poor choice of what to link to is that the automatic links look, by default, like normal links. So readers of my web pages think that I put in the odd links myself. Google's AdWords works much better, providing links to relevant advertisements and clearly differentiating the advertisements from the content of the web pages.
When I first saw Context Links I was worried as I already had a student programming something similar. But the student will not have to do much to do better than Amazon Context Links.