ken_b - 6:52 pm on Nov 30, 2010 (gmt 0)
[added: I see you found it]
Where does Google say that?
You can opt out of showing ads that are based on user interest and demographic categories (for example, 'sports enthusiasts' or 'inferred age:18-34'). In turn, Google will not use visitation information from your sites to help create interest and demographic categories.
However, you cannot opt out of showing ads to users based on their previous interactions with the advertiser, such as visits to an advertiser's website.