I get the question everyday as to why I use Yahoo Publisher Ads as oppose to Google Adsense? For me, it's simple: I make more money with them. Although, since Yahoo Publisher Ads are in their beta phase with the ads, there is a downside in that they do not allow international marketing as the ads are meant only for United States during the beta. This may seem like a problem to some that get good traffic from all over the world as do I, so they have a feature where if an international person views the website the ads just will not appear. So, Yes you could be missing out on some revenue from some clicks international but I have seen more money come in from Publisher Ads than I ever did with Google Adsense.
I think people are becoming immune to all the spammy looking Adsense sites, and I have a feeling eventually the same thing will probably happen with the Yahoo Ads but for now they are really working well for me.
The Yahoo Publisher Ads are also a great alternative to those who for no reason at all have been cancelled out of the Google Adsense program. (Now I realize there are some that deserve to be out of the program, but there are some as well that get booted out for no reason at all even when complying to all the rules and regulations.) I think Google needs to get a better way to track stuff like this, because with their almost zero tolerance policy a lot of people that are good, honest Adsense users are being punished unjustly. And, the thing that drives me mad is when I see these spammy adsense sites that are clearly in violation of the TOS Google has set, and they are still out there making money..
So again, I realize that Yahoo Publisher Ads are just in their Beta Phase (and things could change), but for me right now its the best fit and I am more happy (making more money) with Yahoo Publisher Ads then I ever was with Google Adsense.