Wonderful site with plenty of useful content! As long as you have excellent content, money can be made in different ways like donations, advertising and perhaps money sponsored from VCs.
They did have a donation campaign a while ago I was watching it grow.. and it grew really fast each hour... so yes, lots of people who be more than happy to contribute monetary funds to Wikipedia.
Donation is way of Wikipedia survival. In fact, it starts to face financial problems if it does not have more income from other ways.
Wikipedia a US-registered 501(c)(3) tax-deductible nonprofit charity: The biggest multilingual free-content encyclopedia on the Internet. Over 7 million articles in over 200 languages, and still growing. they only work with donations, dont have any adsense there, not any hidden advertisment policy. they make enough with donations.
They make more than enough money from donation; I guess the figure is some where given on the Wikipedia.
here is the 2006 financial statement of wikipedia, for a non profit organization they are doing quite nice and dont really need adsense. http://upload.wikimedia.org/wikipedia/foundation/2/28/Wikimedia_2006_fs.pdf
They are a not-for-profit and will be for a long time. That definitely helps in them keeping such a devoted community of volunteers.