If you follow Adsense you have seen that if you have a 336x280 ad slot on your website and Google determines that a 300x250 ad will make more money (or there is a 300x250 available but no 336x280 available) it will put the smaller ad in the bigger spot. Google has even recommended the bigger spots because it allows the flexibility for either of those ad units to be placed. I was surprised then recently when I got one of their automated messages saying that I could increase my revenue by 10% per week by replacing the 336x280 with a 300x250 ad. So I'm not sure if this "recommendation" was customized for my particular situation or whether one side of their organization is not talking to the other side.
I'm getting the same thing - Google wants all my 336 ads replaced with 300. I'm OK with that. If I can have a smaller ad with the same (or better) money that bring it on.
yep! same thing happening to all my ads, no bad thing as many wordpress layouts are set up for 300px ads rather than 336px which can be too big to fit in a lot of templates. Does this indicate they might be shutting down that ad size?