I've added Google Adsense adverts to the bottom of each page of the Wiki as an experiment both to get some revenue to help with funding the Wiki (as very few people are using the Amazon Associates link to buy books) and also to see how it works for future sites.
It's fascinating to watch Google try to put in adverts which are appropriate to the page content. It seems to work particularly well (sometimes) in the recommendations pages and it's actually bringing in a moderate amount of income thus far.