Seems like a good idea... Unlike other sites where you can offset your carbon footprint but don't know where the money is exactly going, the PopTech Carbon Initiative will allow you to decide which project your money is going towards. Currently, they offer three choices and all allegedly “allow you to make a fundamental change in someone's life in another part of the world.” Anyone with an eBay account can participate and the site will be up until the end of the year. Overall, I feel it is a cool site and a legitimate effort by eBay to contribute.
The three endorsed carbon-offsetting non-governmental organizations: