Msg#: 3540191 posted 8:54 am on Jan 4, 2008 (gmt 0)
I think it depends on your goals and self-understanding.
Personally, I feel that two Adsense blocks already give a page a cheap look. And most sites with three Adsense blocks look definitely cheap.
If this is not your concern, I'd say go for three ad blocks, check whether your eCPM improves, and make a final decision after the trial. That's the beauty of Adsense - you can just try anything without hurting anyone.