I don't know if the Ads work, but the API in general does. Leaderboards and achievements worked well in a little game I'm making, which I think is awesome. Being able to use Ads with that API would be very nice, specially if there's a way to set the Ad program you want to use.
The clay.io plugin makes everything so simple. I really like it. I still don't know how to personalize the way it looks, though.