AdSensePro of Google starts off an interesting discussion in a Google Groups pointing the community to a recent post made in the Inside AdSense blog. In the blog post, the AdSense team says that it is not permitted to encourage clicking of ads because the proceeds will go to charity.
We want users to click on ads because they are interested in the products or services offered by the advertiser, not because they are interested in supporting a site or a charity.
Remember, the advertiser pays for those clicks, so it would not be fair to encourage this on the advertiser's dime. If you're interested in clicking on ads for charity, I suggest you visit The Hunger Site and its associated rings of sites.
Forum discussion continues at Google Groups.