Months ago, I more or less was forced to turn off most of advertising at YSM due to the low quality of 3rd part traffic and the inability to block it. Certain unknown 3rd party sites were sending 4-5 times the traffic of Yahoo.com.
The performance is better since you can now exclude the 'partners' that are sending you low quality traffic. You do have to weed them out by hand and there is a limit of 250 domains you can exclude. But it has certainly helped a lot.
Will Yahoo send you a list of domains by clicks? My client's website does not have the ability to see the referring partners. Or does someone have say the Top 10 referring domains by YSM they could share and I will just block those :)
If you don't mind waiting until after you've been charged for the traffic, the block domains feature is great. Unfortunately I almost filled mine using only a month's worth of logs. Still seems that simply allowing me to opt out and let me decide where my money gets spent would be a more efficient solution (albeit, less profitable for YSM).