I always knew behavioural targeting advertising works, why? because all the best work that has had the best response either through buying a product or getting a quote has come from ads I have done that is target specific, the last two campaigns for Blackmores and ANZ credit card the response rate was nearly 3 times higher than the average and a much more cost effective approach than the standard approach of 'spray and pray' which I personally hate. One thing that was interesting was that targeted groups were willing to have their browsing history monitored so long as no personal details were stored.