The New York Times has more information on the often awful balance between editorial content and adverts in The Cost of Mobile Ads on 50 News Websites.
The difference was easy to spot: many websites loaded faster and felt easier to use. Data is also expensive. We estimated that on an average American cell data plan, each megabyte downloaded over a cell network costs about a penny. Visiting the home page of Boston.com every day for a month would cost the equivalent of about $9.50 in data usage just for the ads.