Things They Should Invent: an "I don't want to see this ad any more" option
for web browsers

It would put a cookie in your browser telling ad servers not to show you
particular ads. This would be no loss to the advertisers because obviously
users aren't going to click on an ad that they don't want to see, and it
would make users' browsing experience more pleasant.

I use WebWasher to achieve this at home, but I'm not allowed to install
software on my work computer and I really would like a way to avoid seeing
ads for Spiderman, dating services, and pornographic screensavers while at
work.