Wikipedia Advertising Shows Up on Google from Micro Persuations covers how Wikipedia is apparently advertising content on Google. A search on crowdsourcing in Google brings up a Wikipedia ad in the sponsored listing area that says:
1. Harness this exciting wave.
2. Save money or make money!
Yes, the same landing page is shown on the organic listings as well. So why would the Wikipedia be spending money on those ads? Is it even Wikipedia who is purchasing those ads? Maybe it is a 3rd party that is interested in getting more content added to certain Wikipedia pages. Maybe there is some financial interest on that page for some company?
Postscript Barry: ClickZ has a quote from Wayne Saewyc, a Wikimedia spokesperson saying, "As far as I am aware, the Wikimedia Foundation is not purchasing Google ads, or any other advertisements for that matter."