I can not believe they have not done so. It is contextual advertising
and I use it on my movie site and frigging hope Google do! However Kontera are quite good at payouts and only a little behind what Google pays per click. A quote from... http://www.revenews.com/joelcomm/200...t_adsense.html
Kontera has actually been in the keyword business for about six years but their AdLinks program is only now beginning to gather steam. Instead of putting ad units on a Web page and sending ads with some relevance to the site’s content, AdLinks highlights particular words already in a publisher’s text and presents ads in a floating tool tip only when a user mouses over. That means advertisers are getting users with a strong interest in their products, publishers are getting highly targeted ads and users are getting an uninterrupted surfing experience in which calling up ads can actually be fun.
Another company doing this is: www.vibrantmedia.com