Apparently, even though they make you go through the motions of "opting out," it's a waste of time. I've written to them, and here is their reply:
******My Yahoo! is made available in part by the advertising that you view while using our site. While it is our utmost goal to choose ads that would be pleasing to all our users, we understand this may not be thecase at all times and apologize if these advertisements disrupted your experience with us.
As a valued My Yahoo! user, we appreciate that you have taken the time to contact us. Our Product Team is intently reviewing all feedback received which helps us to improve our products and services to better serve you.
To provide additional advertisement feedback in the future, please clickon the "Ad Feedback" link at the bottom of the specific ad you are viewing.******