Google is now using what it calls Behavioral AdWords.
(Using an example from gigaom)
The idea is if you search for Italian Hotels, and then follow that with an additional search for example “weather”, Behavioral AdWords will mix in “Italian Weather related” advertisements in with normal weather related ad’s.
To see it in action try the example searches, search for Italian Hotels and then do a separate search for the keyword “weather”.
The story quotes a roundtable discussion with reporters earlier today from Susan Wojcicki, Google VP Product Management.
“Wojcicki said that no user information is stored by Google, and this is on-the-fly ads that are displayed. Close the window (or the search session), and the relevance goes away, she said.”
This may explain some of the more unusual results that have lately perhaps been attributed to broad match.