Jakob Nielsen’s most recent Alertbox entitled Most Hated Advertising Techniquesprovides some hard data on what many of us have known for a while now — aggressive online ads alienate site visitors out of proportion with the potential upside of clickthroughs.

Here’s a particularly relevant part of the article:

“Users have started to defend themselves against pop-ups. The percentage of users who report using pop-up or ad-blocking software increased from 26% in April 2003 to 69% in September 2004, which is an astonishing growth rate.

Users not only dislike pop-ups, they transfer their dislike to the advertisers behind the ad and to the website that exposed them to it. In a survey of 18,808 users, more than 50% reported that a pop-up ad affected their opinion of the advertiser very negatively and nearly 40% reported that it affected their opinion of the website very negatively.”