Tinus - 4:45 pm on May 20, 2006 (gmt 0)

Another possibility is that Google develops a kind of semantic network. Concepts are used often together on pages/sites, sometimes close to eachother, sometimes far away from eachother. Only thing Google has to do is to use statistics to measure the amount of relatedness between pages/sites with the same concepts on the web.
Hotels and car rent occur often on travel sites so relatedness is high value, hotels and morgages occur nearly never together so will have a low relatedness value. This is possible to automize but needs a lot of computing power and data.
Maybe the semantic network of Google is will improve over time when it is evaluated with new data.
Anyhow this is how I will interpret relatedness when making links. For the concept Tourism hotels, car rents, musea etc. are relevant. For the concept Vegas Casino's is relevant.