I read on one of Google's training modules that it is alright to have advertisement associated with your articles so long as the advertisement is relevant to the topic. For instance, if you are writing about the benefits of using a microwave oven and you showed ads for microwave ovens and microwave oven parts, then your content to ad relation is relevant and not penalized. On the other hand, if that same article had ads for dental floss, certainly Google would downgrade the page for containing irrelevant ads associated with the content.
Google’s main contention is with pages that do not supply the information readers came to your page to receive. Google wants the reader’s experience to be fulfilling. The reader should leave your page feeling like they received the information and were not bombarded with unnecessary advertisements.