Back in late April, the Yahoo! Publisher Network blog featured a site named TopSpeed.com as sporting the YPN ads on their site.
TopSpeed.com is to car crazies is what HoopsVibe.com is to basketball fans–a space where enthusiasts can read about racing, argue over cars, play driving games, examine auto specs, view videos of car crashes (may favorite page, I have to admit) and more, all in a media- and interaction-rich environment.
But now, if you visit TopSpeed.com you will notice that they have Google AdSense ads live currently. So they must of switched back from Google to Yahoo! and then back from Yahoo! to Google.
Forum discussion at DigitalPoint Forums.