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AdLink as the smallest possible ad on Wikipedia.
I just tested some Wikipedia articles with the AdSense preview tool. Articles where my own pages about the same bring great targeted AdSense ads.
Not so Wikipedia, the preview tool showed only complete irrelevant ads.
wiki is a foundation (non-profit), so it may not even be possible to have ads everywhere.
"A nonprofit organization (abbreviated "NPO", also "non-profit" or "not-for-profit") is a legally constituted organization whose primary objective is to support or to actively engage in activities of public or private interest without any commercial or monetary profit purposes."
Given the amount of money it would make with ads, it could be hard to call it non-profit.
There's an interesting news report on wiki and $$$ [detnews.com] in today's news:
"With around 300 million page views a day, the site by some estimates could be worth many hundreds of millions of dollars if it sold advertising space. It doesn't."
"[Executive Director Sue] Gardner joined Wikipedia nine months ago after leaving the Canadian Broadcasting Co., where she oversaw the introduction in 2006 of advertising on the CBC Web site. She said she didn't foresee a time when Wikipedia would go that route, though she added that she should never say never."
There was proposal for putting only one rotating ad banner for $5 million p/m; which was rejected and discussed to death on both slashdot and offical wiki pages.
Even better, I bet there'd be plenty of companies willing to sponsor Wikipedia to the tune of $20m a year in return for a single graphic or text link bar per page, but hey.. sometimes the principle is worth more than simplicity.