I am asking about this ad size because it's brand new and I haven's seen any report of experience using it. When it is located under/below the fold, what is the average eCPM (RPM) as compared to the other ad units?
As a test, I did put it in place of a 336x280 that was doing well, and the 300x600 did almost was well as the 336x280. I positioned it so that half of it was above the fold and half was below, which I think caused people to scroll down (which they rarely do) and increased CTR. So it can have its uses.
I saw two image ads today in this size...the BIG Banana weight loss ad and another pretty cool one for some email service I'd never heard of. I had to check myself from clicking both of them as they were on one of my sites and I almost forgot.