On my wiki http://krass.com/ I used to solutions for adsense: - I created a skin which adds a small ad on all pages on the lower right corner - in that skin special macros like __GOOGLEAD_SKYSCRAPER__ will be replaced by the google ad (or search). that allows me to place more ads on some pages, if I like.
now I probably would solve the second solution with an extension. But doing it in the skin means that logged in users can switch to an ad free skin if they want so.
christof