I recently added the 300x250 box to my article pages at http://www.brainbucketmagazine.com/News/article/sid=1006.html. That's less than 1/10 of the pages google has indexed for my site. But my sitewide eCPM has increased by over 100% as a result. Those 300x250 boxes well placed work wonders. I disappointed I haven't tried this before Just a thought for those of you looking to increase your revenue.
IIRC, according to Google, the three most effective ads are (in order), the 336*280, 300*250, and 160*600. I saw significant increases after adding these ads to my site. Still, going from a 0% CTR to a 0.5% CTR ain't that great, but I've heard it's worked wonders for other people. I guess something must be wrong with my placement.