Google is making some changes to how the billing works for its Contributor service. Contributer lets you pay to see fewer ads around the web, and from now on, any portion of your monthly contribution that has gone unused will be refunded. So if your contribution is $6.99, and you only use $4.50, you'll be refunded $2.49.
Google announced the changes in an email to Contributors:
At the end of each billing month (except your free month) you'll get a refund for any money that has not been used toward the removal of ads. You've also received a refund for the unused balance for all of the previous billing cycles during the life of your Contributor account.
In addition to the email to current users, Google is also now reflecting this change on the Contributor website.
Previously, the unused portion of your contribution would be put in a balance, and used in later months if you were low on funds relative to your web activity. Early Contriubtor adopters may also notice a refund for the current month's contribution, which is a "thank you" from Google for trying out Contributor in its early stage.
Source: Contributor by Google