I don't know about how carefully they "selected" or if almost everyone got that mail. The fact that it is opt-out rather than opt-in leads me to believe that they think they will earn more by running CPA on my account. ;)
With all the secrecy at Adsense I will never know whether it's in my financial interest - or not - to allow this experiment to continue. I don't believe Google will ever share with me what I would have earned had I taken the other choice. So, why even bother to send the email?
[edited by: martinibuster at 1:52 am (utc) on July 14, 2007]
[edit reason] Removed email quote. [/edit]