I'm absolutely opposed to ads appearing anywhere on Wikipedia or any commercially-influenced content for that matter. Jimbo says that people will question "why miss out on all that revenue?" To me this is a backwards way of looking at the question of ads. I say "why risk introducing ads if they are not really needed?" Some argue they are "needed" because the foundation needs more money. If this is the case, then the question should be "how can Wikimedia generate revenue?"
Given the large number of reasons why there should not be ads (I won't repeat all of them), Wikipedia and the Wikimedia foundation should be funded by donations or other sources which can have no special influence over the content. The donors ought to including big corporations, again with no special privileges to commercially influence Wikipedia. These corporations would be ones which derive value from Wikipedia by the mere fact that it exists and has thousands of editors worldwide; whose business model depends on the existence of Wikipedia, and the Wikipedia community which encourages many individual contributions. [Recently, Lisa Lynch blogged about why Google and Yahoo commercially benefit from Wikipedia and this is a very important perspective. Wikipedia is very useful for microscale data mining/analysis (regardless of what value it might have for the individual readership)http://www.futureofthebook.org/blog/archives/2005/12/why_google_and.html]. Why shouldn't the companies making money from the Wikipedia data at the microscale should be the primary funders of Wikipedia?
Lisa