I first read the info on Nicolas Quentin's blog OuiLeO.cOm and found this an amazing initiative.
The idea is pretty simple and efficient. You only need to write a short blog post about the programme “My blog is carbon neutral” and include one of their proposed buttons below on your site (see mine on the side bar). Then you send the link to your blog to CO2email@example.com and they plant a tree for you, neutralising the carbon dioxide emissions of your blog. The trees will be planted in the spring of 2010 by the Arbor Day Foundation.
For more information about how and where the trees are planted, visit http://www.kaufda.de/umwelt/carbon-neutral/what-we-do/
It's easy and really worth it... so spread the word!