I have to admit that up until now, I have not heard of Google Contribute. It’s a product that has been out in some sort of a beta form for a few months now and it allows its users to suppress some % of ads for a monthly fee ($2 – 10/month). Essentially, the amount you “contribute” is used to bid against other advertisers for the space where the ad would have ordinarily appeared. You then get an ad-free experience, while the site still does not lose out on potential revenue.
Harris Schachter of Optimizeprime.com has a full review of the product, which I think is worth reading: http://optimizepri.me/google-contribute