Ad routing: matching an ad - display or text - with a publisher web page and user, based on ad category / user search keyword or user profile / landing page category. This is based on relevancy algorithms.
Collaborative filtering: recommendation engines, e.g. for a social network, tell members that "you should join these groups b/c people with same profile join these groups".
Detect conversion rates for new keywords with no historical data; keyword bid optimization. Find new keywords for ad campaigns. Advertising mix optimization.
Botnet detection using linkage analysis and association detection.
Techniques: cloud computing, clustering large sparse dissimilarity matrices, scoring, SVM, boosted and hidden decision trees, ridge regression, etc.