Please no one interpret my comment here as endorsing this concept. I'm merely making a technical comment to help further the discussion.
Carl Witty wrote:
I don't know how much ad space is worth, so this is probably way too much effort for way too little money, but how about this:
en.wikipedia.org gets a sister site en.ads.wikipedia.org (or .com). This is exactly the same, except that it serves ads. Part of the "how to donate" links explain that you can give wikipedia a little extra money by browsing the with-ads version. Every page on the with-ads version has a link to the corresponding without-ads page ("Click _here_ to see this site without the ads"). The with-ads version sets up robots.txt to avoid search engines.
This scheme could be implemented more cleanly by using a cookie rather than a separate domain. A person visiting the donate page could find a link to set a cookie that says 'ads=true'. After that, they would see ads until they turned them off. Alternatively, this could be an option in user preferences.
I think that the amount of money that such a setup would generate would be extremely tiny, since most people would not ever even see the link. The vast majority of pageviews on the site are people surfing in randomly from all over the web.
Even so, I will say that from a technical perspective this would not be hard to setup fairly seamlessly.
--Jimbo