Would you let someone else decide what content is relevant to your site?
Fizzylab has a proprietary Relevance Engine(tm) that promises not to search based on keywords, but rather to match themes or concepts for its users. The technology is mostly being used to allow "related articles" buttons to analyze a large database of articles and then link to the few that are actually relevant. You'll have to click to find out if it works.
If you are interested in how an AI could potentially match context, see this paper.
I'm more interested in the possibilities of cross-site sharing (in something resembling real time). So, if there were a Gnutella like system that could every morning pull article headlines off Infolets and the sites that Infolets trusts and could then populate a designated section of your webpage with links to the articles from those site that are relevant to the current content of your webpage, would you use it?
P.S. My company, KarateDepot.com, sells through Vendio but we don't use their (or anyone else's) context matching technology on our site.