Adam pointed me to a post he wrote about CPC RSS ads today which is a bit shocking.
Turns out Yahoo’s (and probably Google’s) mechanism for serving ads is fundamentally broken. In a nutshell the ad image serves a cookie. This cookie is then stored in your aggregator and requested when you click the link.
If the user doesn’t have the cookie then you don’t get paid. Not only that but the ad doesn’t load as it redirects you to publisher.yahoo.com.
There’s a non-trivial percentage of users that have this problem. If you run NetNewsWire and use FireFox as your browser you’re certainly one of them. Granted there’s a significant percentage of people using Bloglines which wouldn’t encounter this issue.