I found this fascinating quote today:

 

It’s clear that display advertising, despite a lack of clicks, can have a significant positive impact on: – Visitation to the advertiser’s Web site (lift of at least 46% over a four week period) – The likelihood of consumers conducting a search query using the advertiser’s branded terms  (a lift of at least 38% over a four week period) – Consumers’ likelihood of buying the advertised brand online (an average 27% lift in online sales)  – Consumers’ likelihood of buying at the advertiser’s retail store (an average lift of 17%)

A VC, Dec 2008

 

You should read the whole article.