We already know that almost nothing comes for free and if you're getting something for free in the world of IT this normally means that your being served up advertising or you are trading your personal data for the purpose of advertising, people differ in their opinion on that, I have heard it said "I love adds because that means that I don't have to pay for the service", others prefer a traditional model where they can just purchase whatever it is and get on with things without interruption. However antivirus manufacturer AVG has sent a few ripples through the tech industry by announcing that if you use their free antivirus product they will collect sell your data, however the data will not be personally identifiable. If you use AVG free for home PC's for example here are some resources to help you consider if your happy with the change.
http://news.softpedia.com/news/avg-proudly-announces-it-will-sell-your-browsing-history-to-online-advertisers-492146.shtml
http://now.avg.com/understanding-the-new-privacy-policy/
http://www.avg.com/gb-en/privacy-new