I sarted running a few pages with Yahoo ads a week ago. I've been running AdSense for a couple of years now, but Yahoo called me on the phone and asked if I'd be interested in trying their ads, so I said I would. I put Yahoo ads on a few pages that have a couple of years of AsSense stats available, so I have a good idea of how those pages performed with AdSense.
My site deals with various types of consumer electronics and technology.
These are my thoughts so far:
(1) Why the hell do their banner (468x60) and 1/2 banner ads have no text and just the headline link? I don't want ads that simply read "Free Shipping!" with no indication of what's being shipped? A called them and asked them what's going on with that and their reply was that they would look into it. I then got email that boiled down to, "that's the way we do it". Not good enough. Most of my ad space is in that format so it now excludes 90% of my site from Yahoo.
(2) Ad targeting (even with the page topic suggested) is poor. On a page about electronics I still get ads for dog walking and dating services.
(3) Even the targeted ads aren't very interesting to me or my viewers since CTR has dropped way off from AdSense
(4) Their reporting stats are inferior to AdSense.
(5) The saving grace is that the few clicks that I do get pay much higher than AdSense. Maybe 5x higher on average, so that with 1/5th the CTR I generate about the same revenue per page.
Overall I'm not very impressed, though I'd love to get the revenue per click that I'm getting from Yahoo on my Google ads!
They're going to have to do a hell of a lot better to move me away from AdSense, even though my AdSense revenue has been falling recently despite increasing traffic and the same CTR. I'm not very happy with AdSense because of falling revenue, but I'm even less happy with Yahoo because of their poor targeting, limited stats and lack of usable banner format ads.